From 5d25bd3d1bac1a02c4b5c4c97a11607e971d32b3 Mon Sep 17 00:00:00 2001
From: Jakub Freisler <jakub@frsource.org>
Date: Mon, 16 Dec 2024 03:35:52 +0100
Subject: [PATCH 01/15] feat: add `prefer-class-fields` rule

---
 docs/rules/prefer-class-fields.md           |  41 ++++++
 readme.md                                   |   1 +
 rules/prefer-class-fields.js                | 111 +++++++++++++++
 test/prefer-class-fields.mjs                |  86 +++++++++++
 test/snapshots/prefer-class-fields.mjs.md   | 149 ++++++++++++++++++++
 test/snapshots/prefer-class-fields.mjs.snap | Bin 0 -> 642 bytes
 6 files changed, 388 insertions(+)
 create mode 100644 docs/rules/prefer-class-fields.md
 create mode 100644 rules/prefer-class-fields.js
 create mode 100644 test/prefer-class-fields.mjs
 create mode 100644 test/snapshots/prefer-class-fields.mjs.md
 create mode 100644 test/snapshots/prefer-class-fields.mjs.snap

diff --git a/docs/rules/prefer-class-fields.md b/docs/rules/prefer-class-fields.md
new file mode 100644
index 0000000000..e14478eddd
--- /dev/null
+++ b/docs/rules/prefer-class-fields.md
@@ -0,0 +1,41 @@
+# Prefer class field declarations over assigning static values in constructor using `this`
+
+💼 This rule is enabled in the ✅ `recommended` [config](https://github.com/sindresorhus/eslint-plugin-unicorn#preset-configs-eslintconfigjs).
+
+🔧 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
+
+<!-- end auto-generated rule header -->
+<!-- Do not manually modify this header. Run: `npm run fix:eslint-docs` -->
+
+This rule will enforce the use of field declarations over `this` assignments in contructors for static values.
+
+> To avoid leaving empty constructors after autofix use [`no-useless-contructor` rule](https://eslint.org/docs/latest/rules/no-useless-constructor).
+
+## Fail
+
+```js
+class Foo {
+  constructor() {
+    this.foo = 'foo';
+  }
+}
+
+class MyError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = "MyError";
+  }
+}
+```
+
+## Pass
+
+```js
+class Foo {
+  foo = 'foo';
+}
+
+class MyError extends Error {
+  name = "MyError"
+}
+```
diff --git a/readme.md b/readme.md
index b1f5d022c3..9147209d7a 100644
--- a/readme.md
+++ b/readme.md
@@ -181,6 +181,7 @@ If you don't use the preset, ensure you use the same `env` and `parserOptions` c
 | [prefer-array-some](docs/rules/prefer-array-some.md)                                             | Prefer `.some(…)` over `.filter(…).length` check and `.{find,findLast,findIndex,findLastIndex}(…)`.                                                                                                               | ✅  | 🔧 | 💡 |
 | [prefer-at](docs/rules/prefer-at.md)                                                             | Prefer `.at()` method for index access and `String#charAt()`.                                                                                                                                                     | ✅  | 🔧 | 💡 |
 | [prefer-blob-reading-methods](docs/rules/prefer-blob-reading-methods.md)                         | Prefer `Blob#arrayBuffer()` over `FileReader#readAsArrayBuffer(…)` and `Blob#text()` over `FileReader#readAsText(…)`.                                                                                             | ✅  |    |    |
+| [prefer-class-fields](docs/rules/prefer-class-fields.md)                                         | Prefer class field declarations over assigning static values in constructor using `this`.                                                                                                                         | ✅  | 🔧 |    |
 | [prefer-code-point](docs/rules/prefer-code-point.md)                                             | Prefer `String#codePointAt(…)` over `String#charCodeAt(…)` and `String.fromCodePoint(…)` over `String.fromCharCode(…)`.                                                                                           | ✅  |    | 💡 |
 | [prefer-date-now](docs/rules/prefer-date-now.md)                                                 | Prefer `Date.now()` to get the number of milliseconds since the Unix Epoch.                                                                                                                                       | ✅  | 🔧 |    |
 | [prefer-default-parameters](docs/rules/prefer-default-parameters.md)                             | Prefer default parameters over reassignment.                                                                                                                                                                      | ✅  | 🔧 | 💡 |
diff --git a/rules/prefer-class-fields.js b/rules/prefer-class-fields.js
new file mode 100644
index 0000000000..bcaae2f9b9
--- /dev/null
+++ b/rules/prefer-class-fields.js
@@ -0,0 +1,111 @@
+'use strict';
+const getIndentString = require('./utils/get-indent-string.js');
+
+const MESSAGE_ID = 'prefer-class-fields/error';
+const messages = {
+	[MESSAGE_ID]:
+		'Prefer class field declaration over `this` assignment in constructor for static values.',
+};
+
+/**
+ * @param {import('eslint').Rule.Node} node
+ * @returns {node is import('estree').ExpressionStatement & {expression: import('estree').AssignmentExpression & {left: import('estree').MemberExpression & {object: import('estree').ThisExpression}}}}
+ */
+const isThisAssignmentExpression = node => {
+	if (
+		node.type !== 'ExpressionStatement'
+		|| node.expression.type !== 'AssignmentExpression'
+	) {
+		return false;
+	}
+
+	const lhs = node.expression.left;
+
+	if (!lhs.object || lhs.object.type !== 'ThisExpression') {
+		return false;
+	}
+
+	return true;
+};
+
+/**
+ * @template Array
+ * @param {Array} array
+ * @returns {Array}
+ */
+const reverseArray = array => [...array].reverse();
+
+/**
+ * @param {import('eslint').Rule.Node} node
+ * @param {import('eslint').Rule.RuleContext['sourceCode']} sourceCode
+ * @param {import('eslint').Rule.RuleFixer} fixer
+ */
+const removeThisFieldAssignment = (node, sourceCode, fixer) => {
+	const {line} = node.loc.start;
+	const nodeText = sourceCode.getText(node);
+	const lineText = sourceCode.lines[line - 1];
+	const isOnlyNodeOnLine = lineText.trim() === nodeText;
+
+	return isOnlyNodeOnLine
+		? fixer.removeRange([
+			sourceCode.getIndexFromLoc({line, column: 0}),
+			sourceCode.getIndexFromLoc({line: line + 1, column: 0}),
+		])
+		: fixer.remove(node);
+};
+
+/** @type {import('eslint').Rule.RuleModule['create']} */
+const create = context => {
+	const {sourceCode} = context;
+
+	return {
+		ClassBody(node) {
+			const constructor = node.body.find(x => x.kind === 'constructor');
+
+			if (!constructor || constructor.type !== 'MethodDefinition') {
+				return;
+			}
+
+			const constructorBody = constructor.value.body.body;
+			const classBodyStartRange = [node.range[0], node.range[0] + 1];
+			const indent = getIndentString(constructor, sourceCode);
+
+			for (const node of reverseArray(constructorBody)) {
+				if (
+					isThisAssignmentExpression(node)
+					&& node.expression.right?.type === 'Literal'
+				) {
+					return {
+						node,
+						messageId: MESSAGE_ID,
+
+						/** @param {import('eslint').Rule.RuleFixer} fixer */
+						* fix(fixer) {
+							yield removeThisFieldAssignment(node, sourceCode, fixer);
+							yield fixer.insertTextAfterRange(
+								classBodyStartRange,
+								`\n${indent}${node.expression.left.property.name} = ${node.expression.right.raw};`,
+							);
+						},
+					};
+				}
+			}
+		},
+	};
+};
+
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+	create,
+	meta: {
+		type: 'suggestion',
+		docs: {
+			description:
+				'Prefer class field declarations over assigning static values in constructor using `this`.',
+			recommended: true,
+		},
+		fixable: 'code',
+		hasSuggestions: false,
+		messages,
+	},
+};
diff --git a/test/prefer-class-fields.mjs b/test/prefer-class-fields.mjs
new file mode 100644
index 0000000000..ef827cd1ff
--- /dev/null
+++ b/test/prefer-class-fields.mjs
@@ -0,0 +1,86 @@
+import outdent from 'outdent';
+import {getTester} from './utils/test.mjs';
+
+const {test} = getTester(import.meta);
+
+const MESSAGE_ID = 'prefer-class-fields/error';
+
+test.snapshot({
+	valid: [
+		outdent`
+			class Foo {
+				foo = 'foo';
+			}
+		`,
+		outdent`
+			class MyError extends Error {
+				name = "MyError";
+			}
+		`,
+	],
+	invalid: [
+		outdent`
+			class Foo {
+				constructor() {
+					this.foo = 'foo';
+				}
+			}
+		`,
+		outdent`
+			class Foo {
+				constructor() {
+					this.foo = 'foo';
+					this.foo2 = 'foo2';
+				}
+			}
+		`,
+		outdent`
+			class Foo {
+				constructor(argument) {
+					this.foo = 'foo';
+					this.foo2 = argument + 'test';
+					this.foo3 = 'foo3';
+				}
+			}
+		`,
+		outdent`
+			class MyError extends Error {
+				constructor(message) {
+					super(message);
+					this.name = "MyError";
+				}
+			}
+		`,
+	],
+});
+
+test.typescript({
+	valid: [
+		outdent`
+			class Foo {
+				foo: string = 'foo';
+			}
+		`,
+	],
+	invalid: [
+		{
+			code: outdent`
+				class MyError extends Error {
+					constructor(message: string) {
+						super(message);
+						this.name = "MyError";
+					}
+				}
+			`,
+			errors: [{messageId: MESSAGE_ID}],
+			output: outdent`
+				class MyError extends Error {
+					name = "MyError";
+					constructor(message: string) {
+						super(message);
+					}
+				}
+			`,
+		},
+	],
+});
diff --git a/test/snapshots/prefer-class-fields.mjs.md b/test/snapshots/prefer-class-fields.mjs.md
new file mode 100644
index 0000000000..39fde7e9e7
--- /dev/null
+++ b/test/snapshots/prefer-class-fields.mjs.md
@@ -0,0 +1,149 @@
+# Snapshot report for `test/prefer-class-fields.mjs`
+
+The actual snapshot is saved in `prefer-class-fields.mjs.snap`.
+
+Generated by [AVA](https://avajs.dev).
+
+## invalid(1): class Foo { constructor() { this.foo = 'foo'; } }
+
+> Input
+
+    `␊
+      1 | class Foo {␊
+      2 | 	constructor() {␊
+      3 | 		this.foo = 'foo';␊
+      4 | 	}␊
+      5 | }␊
+    `
+
+> Output
+
+    `␊
+      1 | class Foo {␊
+      2 | 	foo = 'foo';␊
+      3 | 	constructor() {␊
+      4 | 	}␊
+      5 | }␊
+    `
+
+> Error 1/1
+
+    `␊
+      1 | class Foo {␊
+      2 | 	constructor() {␊
+    > 3 | 		this.foo = 'foo';␊
+        | 		^^^^^^^^^^^^^^^^^ Prefer class field declaration over \`this\` assignment in constructor for static values.␊
+      4 | 	}␊
+      5 | }␊
+    `
+
+## invalid(2): class Foo { constructor() { this.foo = 'foo'; this.foo2 = 'foo2'; } }
+
+> Input
+
+    `␊
+      1 | class Foo {␊
+      2 | 	constructor() {␊
+      3 | 		this.foo = 'foo';␊
+      4 | 		this.foo2 = 'foo2';␊
+      5 | 	}␊
+      6 | }␊
+    `
+
+> Output
+
+    `␊
+      1 | class Foo {␊
+      2 | 	foo = 'foo';␊
+      3 | 	foo2 = 'foo2';␊
+      4 | 	constructor() {␊
+      5 | 	}␊
+      6 | }␊
+    `
+
+> Error 1/1
+
+    `␊
+      1 | class Foo {␊
+      2 | 	constructor() {␊
+      3 | 		this.foo = 'foo';␊
+    > 4 | 		this.foo2 = 'foo2';␊
+        | 		^^^^^^^^^^^^^^^^^^^ Prefer class field declaration over \`this\` assignment in constructor for static values.␊
+      5 | 	}␊
+      6 | }␊
+    `
+
+## invalid(3): class Foo { constructor(argument) { this.foo = 'foo'; this.foo2 = argument + 'test'; this.foo3 = 'foo3'; } }
+
+> Input
+
+    `␊
+      1 | class Foo {␊
+      2 | 	constructor(argument) {␊
+      3 | 		this.foo = 'foo';␊
+      4 | 		this.foo2 = argument + 'test';␊
+      5 | 		this.foo3 = 'foo3';␊
+      6 | 	}␊
+      7 | }␊
+    `
+
+> Output
+
+    `␊
+      1 | class Foo {␊
+      2 | 	foo = 'foo';␊
+      3 | 	foo3 = 'foo3';␊
+      4 | 	constructor(argument) {␊
+      5 | 		this.foo2 = argument + 'test';␊
+      6 | 	}␊
+      7 | }␊
+    `
+
+> Error 1/1
+
+    `␊
+      1 | class Foo {␊
+      2 | 	constructor(argument) {␊
+      3 | 		this.foo = 'foo';␊
+      4 | 		this.foo2 = argument + 'test';␊
+    > 5 | 		this.foo3 = 'foo3';␊
+        | 		^^^^^^^^^^^^^^^^^^^ Prefer class field declaration over \`this\` assignment in constructor for static values.␊
+      6 | 	}␊
+      7 | }␊
+    `
+
+## invalid(4): class MyError extends Error { constructor(message) { super(message); this.name = "MyError"; } }
+
+> Input
+
+    `␊
+      1 | class MyError extends Error {␊
+      2 | 	constructor(message) {␊
+      3 | 		super(message);␊
+      4 | 		this.name = "MyError";␊
+      5 | 	}␊
+      6 | }␊
+    `
+
+> Output
+
+    `␊
+      1 | class MyError extends Error {␊
+      2 | 	name = "MyError";␊
+      3 | 	constructor(message) {␊
+      4 | 		super(message);␊
+      5 | 	}␊
+      6 | }␊
+    `
+
+> Error 1/1
+
+    `␊
+      1 | class MyError extends Error {␊
+      2 | 	constructor(message) {␊
+      3 | 		super(message);␊
+    > 4 | 		this.name = "MyError";␊
+        | 		^^^^^^^^^^^^^^^^^^^^^^ Prefer class field declaration over \`this\` assignment in constructor for static values.␊
+      5 | 	}␊
+      6 | }␊
+    `
diff --git a/test/snapshots/prefer-class-fields.mjs.snap b/test/snapshots/prefer-class-fields.mjs.snap
new file mode 100644
index 0000000000000000000000000000000000000000..708c7022c00767eb63068ae80f2e7d9b47cfa28e
GIT binary patch
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zJx)h;JYi-W1vL?i!isHIte_l#V{ij*zzsM6a%wl8c*aR2s(6<fXWskY|NR<&4^JZQ
zpUF>GR52CNQHRAt60u;rx$^{mM5M$4=QxMYW2r>qD=xNoa1M3K<X*@*I%tHPH=bgG
z36n7y$WyN5#Z?dxMc(*#YWHgC<J_%nI<H-ziE;5@7ieLO`rP?0;HAs;l8y_s)18S6
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z{ncpuvjT1QY`T@%SV+887L7raSsdjodKD}Z(MwX{#Z2aJViyfXr7CQD**`oRvOl%H
zd|R?F1#c^|TlSjARyTOglAK2R*oOEIt%S>p5-g1Cf+fcFV)vIT$!J>}i6iHMX8gXh
zhU~kQ*{@@SjKP&h=qw+h_RR>r_;CFe9Vr?I64$@<q3Tm9Nsp#8C6fW2Eo37TlRiZU
zTiID#mZ|xwb?%FfoW+N!moqyzt(>!^H?m}JsXO3ObNhKEw<g8XH-}b6+fv5jOXA4c
c)SPZOx0q{pQLa|_*LsEg0~2#he*g;r0O-atr2qf`

literal 0
HcmV?d00001


From bb42087fd34c4a53bdfd50075882c166467ed0a5 Mon Sep 17 00:00:00 2001
From: Jakub Freisler <jakub@frsource.org>
Date: Mon, 16 Dec 2024 03:52:15 +0100
Subject: [PATCH 02/15] fix: handle edge case of constructor without body

fixup "contructor" typos
---
 docs/rules/prefer-class-fields.md | 4 ++--
 rules/prefer-class-fields.js      | 7 ++++++-
 test/prefer-class-fields.mjs      | 5 +++++
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/docs/rules/prefer-class-fields.md b/docs/rules/prefer-class-fields.md
index e14478eddd..2149b70616 100644
--- a/docs/rules/prefer-class-fields.md
+++ b/docs/rules/prefer-class-fields.md
@@ -7,9 +7,9 @@
 <!-- end auto-generated rule header -->
 <!-- Do not manually modify this header. Run: `npm run fix:eslint-docs` -->
 
-This rule will enforce the use of field declarations over `this` assignments in contructors for static values.
+This rule will enforce the use of field declarations over `this` assignments in constructors for static values.
 
-> To avoid leaving empty constructors after autofix use [`no-useless-contructor` rule](https://eslint.org/docs/latest/rules/no-useless-constructor).
+> To avoid leaving empty constructors after autofix use [`no-useless-constructor` rule](https://eslint.org/docs/latest/rules/no-useless-constructor).
 
 ## Fail
 
diff --git a/rules/prefer-class-fields.js b/rules/prefer-class-fields.js
index bcaae2f9b9..fd4edefabe 100644
--- a/rules/prefer-class-fields.js
+++ b/rules/prefer-class-fields.js
@@ -66,7 +66,12 @@ const create = context => {
 				return;
 			}
 
-			const constructorBody = constructor.value.body.body;
+			const constructorBody = constructor.value.body?.body;
+
+			if (!constructorBody) {
+				return;
+			}
+
 			const classBodyStartRange = [node.range[0], node.range[0] + 1];
 			const indent = getIndentString(constructor, sourceCode);
 
diff --git a/test/prefer-class-fields.mjs b/test/prefer-class-fields.mjs
index ef827cd1ff..5600a8b0b1 100644
--- a/test/prefer-class-fields.mjs
+++ b/test/prefer-class-fields.mjs
@@ -61,6 +61,11 @@ test.typescript({
 				foo: string = 'foo';
 			}
 		`,
+		outdent`
+			declare class Foo {
+				constructor(foo?: string);
+			}
+		`,
 	],
 	invalid: [
 		{

From cd95420111cf8587c3f495cf86a74a1bceb51d85 Mon Sep 17 00:00:00 2001
From: Sindre Sorhus <sindresorhus@gmail.com>
Date: Wed, 18 Dec 2024 14:42:33 +0100
Subject: [PATCH 03/15] Update prefer-class-fields.md

---
 docs/rules/prefer-class-fields.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/docs/rules/prefer-class-fields.md b/docs/rules/prefer-class-fields.md
index 2149b70616..f8afafb525 100644
--- a/docs/rules/prefer-class-fields.md
+++ b/docs/rules/prefer-class-fields.md
@@ -7,9 +7,9 @@
 <!-- end auto-generated rule header -->
 <!-- Do not manually modify this header. Run: `npm run fix:eslint-docs` -->
 
-This rule will enforce the use of field declarations over `this` assignments in constructors for static values.
+This rule enforces the use of class field declarations for static values, instead of assigning them in constructors using `this`.
 
-> To avoid leaving empty constructors after autofix use [`no-useless-constructor` rule](https://eslint.org/docs/latest/rules/no-useless-constructor).
+> To avoid leaving empty constructors after autofixing, use the [`no-useless-constructor` rule](https://eslint.org/docs/latest/rules/no-useless-constructor).
 
 ## Fail
 

From e5e486dba0c9cdb166ff4c5dd252ac2ed62fe6c2 Mon Sep 17 00:00:00 2001
From: Sindre Sorhus <sindresorhus@gmail.com>
Date: Wed, 18 Dec 2024 14:44:46 +0100
Subject: [PATCH 04/15] Update prefer-class-fields.js

---
 rules/prefer-class-fields.js | 40 ++++++++++++++++++++----------------
 1 file changed, 22 insertions(+), 18 deletions(-)

diff --git a/rules/prefer-class-fields.js b/rules/prefer-class-fields.js
index fd4edefabe..a9c886a863 100644
--- a/rules/prefer-class-fields.js
+++ b/rules/prefer-class-fields.js
@@ -3,14 +3,13 @@ const getIndentString = require('./utils/get-indent-string.js');
 
 const MESSAGE_ID = 'prefer-class-fields/error';
 const messages = {
-	[MESSAGE_ID]:
-		'Prefer class field declaration over `this` assignment in constructor for static values.',
+	[MESSAGE_ID]: 'Prefer class field declaration over `this` assignment in constructor for static values.',
 };
 
 /**
- * @param {import('eslint').Rule.Node} node
- * @returns {node is import('estree').ExpressionStatement & {expression: import('estree').AssignmentExpression & {left: import('estree').MemberExpression & {object: import('estree').ThisExpression}}}}
- */
+@param {import('eslint').Rule.Node} node
+@returns {node is import('estree').ExpressionStatement & {expression: import('estree').AssignmentExpression & {left: import('estree').MemberExpression & {object: import('estree').ThisExpression}}}}
+*/
 const isThisAssignmentExpression = node => {
 	if (
 		node.type !== 'ExpressionStatement'
@@ -29,17 +28,17 @@ const isThisAssignmentExpression = node => {
 };
 
 /**
- * @template Array
- * @param {Array} array
- * @returns {Array}
- */
+@template Array
+@param {Array} array
+@returns {Array}
+*/
 const reverseArray = array => [...array].reverse();
 
 /**
- * @param {import('eslint').Rule.Node} node
- * @param {import('eslint').Rule.RuleContext['sourceCode']} sourceCode
- * @param {import('eslint').Rule.RuleFixer} fixer
- */
+@param {import('eslint').Rule.Node} node
+@param {import('eslint').Rule.RuleContext['sourceCode']} sourceCode
+@param {import('eslint').Rule.RuleFixer} fixer
+*/
 const removeThisFieldAssignment = (node, sourceCode, fixer) => {
 	const {line} = node.loc.start;
 	const nodeText = sourceCode.getText(node);
@@ -54,7 +53,9 @@ const removeThisFieldAssignment = (node, sourceCode, fixer) => {
 		: fixer.remove(node);
 };
 
-/** @type {import('eslint').Rule.RuleModule['create']} */
+/**
+@type {import('eslint').Rule.RuleModule['create']}
+*/
 const create = context => {
 	const {sourceCode} = context;
 
@@ -84,7 +85,9 @@ const create = context => {
 						node,
 						messageId: MESSAGE_ID,
 
-						/** @param {import('eslint').Rule.RuleFixer} fixer */
+						/**
+      						@param {import('eslint').Rule.RuleFixer} fixer
+	    					*/
 						* fix(fixer) {
 							yield removeThisFieldAssignment(node, sourceCode, fixer);
 							yield fixer.insertTextAfterRange(
@@ -99,14 +102,15 @@ const create = context => {
 	};
 };
 
-/** @type {import('eslint').Rule.RuleModule} */
+/**
+@type {import('eslint').Rule.RuleModule}
+*/
 module.exports = {
 	create,
 	meta: {
 		type: 'suggestion',
 		docs: {
-			description:
-				'Prefer class field declarations over assigning static values in constructor using `this`.',
+			description: 'Prefer class field declarations over assigning static values in constructor using `this`.',
 			recommended: true,
 		},
 		fixable: 'code',

From 14025db7a686931f441a38ecf34968d4e1a7c069 Mon Sep 17 00:00:00 2001
From: Jakub Freisler <jakub@frsource.org>
Date: Fri, 20 Dec 2024 01:36:04 +0100
Subject: [PATCH 05/15] perf: iterate over original array instead of copying it
 over and reversing

---
 rules/prefer-class-fields.js | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/rules/prefer-class-fields.js b/rules/prefer-class-fields.js
index a9c886a863..a66cd2f176 100644
--- a/rules/prefer-class-fields.js
+++ b/rules/prefer-class-fields.js
@@ -27,12 +27,6 @@ const isThisAssignmentExpression = node => {
 	return true;
 };
 
-/**
-@template Array
-@param {Array} array
-@returns {Array}
-*/
-const reverseArray = array => [...array].reverse();
 
 /**
 @param {import('eslint').Rule.Node} node
@@ -60,8 +54,8 @@ const create = context => {
 	const {sourceCode} = context;
 
 	return {
-		ClassBody(node) {
-			const constructor = node.body.find(x => x.kind === 'constructor');
+		ClassBody(classBody) {
+			const constructor = classBody.body.find(x => x.kind === 'constructor');
 
 			if (!constructor || constructor.type !== 'MethodDefinition') {
 				return;
@@ -73,10 +67,11 @@ const create = context => {
 				return;
 			}
 
-			const classBodyStartRange = [node.range[0], node.range[0] + 1];
+			const classBodyStartRange = [classBody.range[0], classBody.range[0] + 1];
 			const indent = getIndentString(constructor, sourceCode);
 
-			for (const node of reverseArray(constructorBody)) {
+			for (let i = constructorBody.length - 1; i >= 0; i--) {
+				const node = constructorBody[i];
 				if (
 					isThisAssignmentExpression(node)
 					&& node.expression.right?.type === 'Literal'

From 21e3cf1a172d1834bb67bbeabe39215cd0d3830e Mon Sep 17 00:00:00 2001
From: Jakub Freisler <jakub@frsource.org>
Date: Fri, 20 Dec 2024 01:40:31 +0100
Subject: [PATCH 06/15] chore: handle only simple assignments

---
 rules/prefer-class-fields.js |  1 +
 test/prefer-class-fields.mjs | 14 ++++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/rules/prefer-class-fields.js b/rules/prefer-class-fields.js
index a66cd2f176..6e317699e5 100644
--- a/rules/prefer-class-fields.js
+++ b/rules/prefer-class-fields.js
@@ -75,6 +75,7 @@ const create = context => {
 				if (
 					isThisAssignmentExpression(node)
 					&& node.expression.right?.type === 'Literal'
+					&& node.expression.operator === '='
 				) {
 					return {
 						node,
diff --git a/test/prefer-class-fields.mjs b/test/prefer-class-fields.mjs
index 5600a8b0b1..8dfcb4dc01 100644
--- a/test/prefer-class-fields.mjs
+++ b/test/prefer-class-fields.mjs
@@ -17,6 +17,20 @@ test.snapshot({
 				name = "MyError";
 			}
 		`,
+		outdent`
+			class Foo {
+				constructor() {
+					this.foo += 'foo';
+				}
+			}
+		`,
+		outdent`
+			class Foo {
+				constructor() {
+					this.foo ??= 'foo';
+				}
+			}
+		`,
 	],
 	invalid: [
 		outdent`

From 110881dc9457d3f5433401997db92e1ca6cec4d8 Mon Sep 17 00:00:00 2001
From: Jakub Freisler <jakub@frsource.org>
Date: Fri, 20 Dec 2024 01:52:36 +0100
Subject: [PATCH 07/15] lint: fix

---
 rules/prefer-class-fields.js | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/rules/prefer-class-fields.js b/rules/prefer-class-fields.js
index 6e317699e5..16fdeda9e2 100644
--- a/rules/prefer-class-fields.js
+++ b/rules/prefer-class-fields.js
@@ -27,7 +27,6 @@ const isThisAssignmentExpression = node => {
 	return true;
 };
 
-
 /**
 @param {import('eslint').Rule.Node} node
 @param {import('eslint').Rule.RuleContext['sourceCode']} sourceCode
@@ -98,9 +97,7 @@ const create = context => {
 	};
 };
 
-/**
-@type {import('eslint').Rule.RuleModule}
-*/
+/** @type {import('eslint').Rule.RuleModule} */
 module.exports = {
 	create,
 	meta: {

From 378f58bf45ea56b930cba9b48f7fbac71e4a2131 Mon Sep 17 00:00:00 2001
From: Jakub Freisler <jakub@frsource.org>
Date: Fri, 20 Dec 2024 01:54:00 +0100
Subject: [PATCH 08/15] chore: spaces to tabs

---
 docs/rules/prefer-class-fields.md | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/docs/rules/prefer-class-fields.md b/docs/rules/prefer-class-fields.md
index f8afafb525..660898df43 100644
--- a/docs/rules/prefer-class-fields.md
+++ b/docs/rules/prefer-class-fields.md
@@ -15,16 +15,16 @@ This rule enforces the use of class field declarations for static values, instea
 
 ```js
 class Foo {
-  constructor() {
-    this.foo = 'foo';
-  }
+	constructor() {
+		this.foo = 'foo';
+	}
 }
 
 class MyError extends Error {
-  constructor(message: string) {
-    super(message);
-    this.name = "MyError";
-  }
+	constructor(message: string) {
+		super(message);
+		this.name = "MyError";
+	}
 }
 ```
 
@@ -32,10 +32,10 @@ class MyError extends Error {
 
 ```js
 class Foo {
-  foo = 'foo';
+	foo = 'foo';
 }
 
 class MyError extends Error {
-  name = "MyError"
+	name = "MyError"
 }
 ```

From 633829c7daf29bd071a2ed371bbee6de5f28cd9a Mon Sep 17 00:00:00 2001
From: Jakub Freisler <jakub@frsource.org>
Date: Fri, 20 Dec 2024 01:56:26 +0100
Subject: [PATCH 09/15] chore: add dynamic field names to valid test cases

---
 test/prefer-class-fields.mjs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/test/prefer-class-fields.mjs b/test/prefer-class-fields.mjs
index 8dfcb4dc01..61c5996e45 100644
--- a/test/prefer-class-fields.mjs
+++ b/test/prefer-class-fields.mjs
@@ -31,6 +31,14 @@ test.snapshot({
 				}
 			}
 		`,
+		outdent`
+			class Foo {
+				something = 'a';
+				constructor() {
+					this[this.something] = 'foo';
+				}
+			}
+		`,
 	],
 	invalid: [
 		outdent`

From 0e6afb3a27ad2de8ccb5dc8cc7dcb2e89261863c Mon Sep 17 00:00:00 2001
From: Jakub Freisler <jakub@frsource.org>
Date: Fri, 20 Dec 2024 02:05:18 +0100
Subject: [PATCH 10/15] feat: support strings and template strings

---
 rules/prefer-class-fields.js                |  66 ++++++++++++++------
 test/prefer-class-fields.mjs                |  14 +++++
 test/snapshots/prefer-class-fields.mjs.md   |  66 ++++++++++++++++++++
 test/snapshots/prefer-class-fields.mjs.snap | Bin 642 -> 726 bytes
 4 files changed, 127 insertions(+), 19 deletions(-)

diff --git a/rules/prefer-class-fields.js b/rules/prefer-class-fields.js
index 16fdeda9e2..f93dcad002 100644
--- a/rules/prefer-class-fields.js
+++ b/rules/prefer-class-fields.js
@@ -27,12 +27,33 @@ const isThisAssignmentExpression = node => {
 	return true;
 };
 
+/**
+@param {import('estree').Expression | import('estree').PrivateIdentifier} node
+*/
+const getPropertyName = node => {
+	if (node.type === 'Identifier') {
+		return node.name;
+	}
+
+	if (node.type === 'Literal') {
+		return `[${node.raw}]`;
+	}
+
+	if (
+		node.type === 'TemplateLiteral'
+		&& node.expressions.length === 0
+		&& node.quasis.length === 1
+	) {
+		return `[\`${node.quasis[0].value.raw}\`]`;
+	}
+};
+
 /**
 @param {import('eslint').Rule.Node} node
 @param {import('eslint').Rule.RuleContext['sourceCode']} sourceCode
 @param {import('eslint').Rule.RuleFixer} fixer
 */
-const removeThisFieldAssignment = (node, sourceCode, fixer) => {
+const removeFieldAssignment = (node, sourceCode, fixer) => {
 	const {line} = node.loc.start;
 	const nodeText = sourceCode.getText(node);
 	const lineText = sourceCode.lines[line - 1];
@@ -72,26 +93,33 @@ const create = context => {
 			for (let i = constructorBody.length - 1; i >= 0; i--) {
 				const node = constructorBody[i];
 				if (
-					isThisAssignmentExpression(node)
-					&& node.expression.right?.type === 'Literal'
-					&& node.expression.operator === '='
+					!isThisAssignmentExpression(node)
+					|| node.expression.right?.type !== 'Literal'
+					|| node.expression.operator !== '='
 				) {
-					return {
-						node,
-						messageId: MESSAGE_ID,
-
-						/**
-      						@param {import('eslint').Rule.RuleFixer} fixer
-	    					*/
-						* fix(fixer) {
-							yield removeThisFieldAssignment(node, sourceCode, fixer);
-							yield fixer.insertTextAfterRange(
-								classBodyStartRange,
-								`\n${indent}${node.expression.left.property.name} = ${node.expression.right.raw};`,
-							);
-						},
-					};
+					continue;
 				}
+
+				const propertyName = getPropertyName(node.expression.left.property);
+				if (!propertyName) {
+					continue;
+				}
+
+				return {
+					node,
+					messageId: MESSAGE_ID,
+
+					/**
+      				@param {import('eslint').Rule.RuleFixer} fixer
+	    			*/
+					* fix(fixer) {
+						yield removeFieldAssignment(node, sourceCode, fixer);
+						yield fixer.insertTextAfterRange(
+							classBodyStartRange,
+							`\n${indent}${propertyName} = ${node.expression.right.raw};`,
+						);
+					},
+				};
 			}
 		},
 	};
diff --git a/test/prefer-class-fields.mjs b/test/prefer-class-fields.mjs
index 61c5996e45..52beae2b7f 100644
--- a/test/prefer-class-fields.mjs
+++ b/test/prefer-class-fields.mjs
@@ -73,6 +73,20 @@ test.snapshot({
 				}
 			}
 		`,
+		outdent`
+			class Foo {
+				constructor() {
+					this['foo'] = 'foo';
+				}
+			}
+		`,
+		outdent`
+			class Foo {
+				constructor() {
+					this[\`foo\`] = 'foo';
+				}
+			}
+		`,
 	],
 });
 
diff --git a/test/snapshots/prefer-class-fields.mjs.md b/test/snapshots/prefer-class-fields.mjs.md
index 39fde7e9e7..d3b6e6ab0e 100644
--- a/test/snapshots/prefer-class-fields.mjs.md
+++ b/test/snapshots/prefer-class-fields.mjs.md
@@ -147,3 +147,69 @@ Generated by [AVA](https://avajs.dev).
       5 | 	}␊
       6 | }␊
     `
+
+## invalid(5): class Foo { constructor() { this['foo'] = 'foo'; } }
+
+> Input
+
+    `␊
+      1 | class Foo {␊
+      2 | 	constructor() {␊
+      3 | 		this['foo'] = 'foo';␊
+      4 | 	}␊
+      5 | }␊
+    `
+
+> Output
+
+    `␊
+      1 | class Foo {␊
+      2 | 	['foo'] = 'foo';␊
+      3 | 	constructor() {␊
+      4 | 	}␊
+      5 | }␊
+    `
+
+> Error 1/1
+
+    `␊
+      1 | class Foo {␊
+      2 | 	constructor() {␊
+    > 3 | 		this['foo'] = 'foo';␊
+        | 		^^^^^^^^^^^^^^^^^^^^ Prefer class field declaration over \`this\` assignment in constructor for static values.␊
+      4 | 	}␊
+      5 | }␊
+    `
+
+## invalid(6): class Foo { constructor() { this[`foo`] = 'foo'; } }
+
+> Input
+
+    `␊
+      1 | class Foo {␊
+      2 | 	constructor() {␊
+      3 | 		this[\`foo\`] = 'foo';␊
+      4 | 	}␊
+      5 | }␊
+    `
+
+> Output
+
+    `␊
+      1 | class Foo {␊
+      2 | 	[\`foo\`] = 'foo';␊
+      3 | 	constructor() {␊
+      4 | 	}␊
+      5 | }␊
+    `
+
+> Error 1/1
+
+    `␊
+      1 | class Foo {␊
+      2 | 	constructor() {␊
+    > 3 | 		this[\`foo\`] = 'foo';␊
+        | 		^^^^^^^^^^^^^^^^^^^^ Prefer class field declaration over \`this\` assignment in constructor for static values.␊
+      4 | 	}␊
+      5 | }␊
+    `
diff --git a/test/snapshots/prefer-class-fields.mjs.snap b/test/snapshots/prefer-class-fields.mjs.snap
index 708c7022c00767eb63068ae80f2e7d9b47cfa28e..fa6d236595b0f1ead9f1fab31ea1fadaa3cfb661 100644
GIT binary patch
literal 726
zcmV;{0xA7LRzV<BZeeh9Xm4~Nb~6eC090$xc(<ubsnSWh8dfhLw~==&wD9Jk(z(Rt
zpgcH@mmiA=00000000Bcmd|d}KoG{`B81{wB_3c@4rzr{lz&A6CE`*f4yYi6)Cv`4
zYp>H)9dFoOM?p=*0l|f9Pn@7U0FS|mD<`hJ0S|zj+DXRVO`NDD%`IzZzHerJlbx^L
zk<XnI`SF}8rhM9Ou%JhL=5Cg^9)RN$Dd92aa0(6&q!OW{xY*o+Q&7iDZhM?V14<s}
zrH3$tA(H{=%44qN`*YVNitIZ#3bzW;$GTZqw_e%+Wf)8cwgD<IfMP1X4N#4aiy0jo
zpcXwD+5mMJz|f{XIify&5_Cfq%N`=xJ+o{oa#e3dE9mWoYNGgST5;`1A%CXL8JWW9
z$?Nn7o(bwv5l8nJ^<8kO;}by?;{os<70`+Twtz^<+Chf~3Rp1RM)0@*sfc0@^oSo)
zxot|7?FzvKl<$=jPM#;6R2JqWIjO`)6%#w}P!r!=B0EKmhdAX??mH%~B(g*o<0_+9
z)0@}Yz_k5EwEbCtHgj#7GizfY@k&|L79z`HKVh*tgGD0RVI(}C$>dGA3nfLRntEJ~
ze^E6d`yKV=OU}Mbd0UX(tk<M$MUCgUlB1H|HzEEFrEoSQ1q0()FvB=bww^B~t!*?C
z2i6^A{I<1%+Bav`eib96EnIelPLdI-jYsI|+l#koU(vvoaPbWfRfkGR+BBLe8FuO9
zARd{3bSN}nBaXFUn3~V1bDuDB1|Pa!PV9_ZnX-i&nX#Aa4md+@KP=={r<mC}P#QHu
z8uKrS18W^QU9+yRuFZLMHNt-_u8>Cw|MeW}%&XC#!r`3F*F&qq{&F{TS}ND_OOWyl
zv$7`o@(b{91l!Lg7hsJgGdZhYgU8(L<l&~}ao+kr+@z!~nVW3%m2;D|bRD_*2jpy4
I(r^y|0BV6!?*IS*

literal 642
zcmV-|0)72KRzV<BZeeh9Xm4~Nb~6eC0PM4X)!+N9p1Uw^jG+zqsA0-=0`W_-d*P=j
zxK0$YY#)mV00000000BUmO*aQKp2JNB81{yB@XaZ7HL(fC~*oBDA`eo1u86%=mONK
zJx)h;JYi-W1vL?i!isHIte_l#V{ij*zzsM6a%wl8c*aR2s(6<fXWskY|NR<&4^JZQ
zpUF>GR52CNQHRAt60u;rx$^{mM5M$4=QxMYW2r>qD=xNoa1M3K<X*@*I%tHPH=bgG
z36n7y$WyN5#Z?dxMc(*#YWHgC<J_%nI<H-ziE;5@7ieLO`rP?0;HAs;l8y_s)18S6
z>|>0HOCxeZBl<iZBr21AtH~bPW#>-z%vOwo;bEd?ioc7B8^3DHSK6(p6w{q|^ABDM
z8d8y+9x@sQ2&f+sK@{UL_>c-5rw1N`NXdF}pT-I-F18UN7m$i5=3_{rgvvczsqC2$
zT%h@|nRD_g=cKhVC;3V%TWZ<Z`KUGV{eNVqZt#$mJgxnajVq~HqN{OL(rcT|8*S*c
z{ncpuvjT1QY`T@%SV+887L7raSsdjodKD}Z(MwX{#Z2aJViyfXr7CQD**`oRvOl%H
zd|R?F1#c^|TlSjARyTOglAK2R*oOEIt%S>p5-g1Cf+fcFV)vIT$!J>}i6iHMX8gXh
zhU~kQ*{@@SjKP&h=qw+h_RR>r_;CFe9Vr?I64$@<q3Tm9Nsp#8C6fW2Eo37TlRiZU
zTiID#mZ|xwb?%FfoW+N!moqyzt(>!^H?m}JsXO3ObNhKEw<g8XH-}b6+fv5jOXA4c
c)SPZOx0q{pQLa|_*LsEg0~2#he*g;r0O-atr2qf`


From a7edb371f78b157570e5c96d6d901c6a653dc8b0 Mon Sep 17 00:00:00 2001
From: Jakub Freisler <jakub@frsource.org>
Date: Fri, 20 Dec 2024 02:48:04 +0100
Subject: [PATCH 11/15] chore: replace existing field if present

---
 rules/prefer-class-fields.js                | 124 ++++++++++++--------
 test/prefer-class-fields.mjs                |  10 +-
 test/snapshots/prefer-class-fields.mjs.md   |  55 ++-------
 test/snapshots/prefer-class-fields.mjs.snap | Bin 726 -> 706 bytes
 4 files changed, 89 insertions(+), 100 deletions(-)

diff --git a/rules/prefer-class-fields.js b/rules/prefer-class-fields.js
index f93dcad002..201e448467 100644
--- a/rules/prefer-class-fields.js
+++ b/rules/prefer-class-fields.js
@@ -27,27 +27,6 @@ const isThisAssignmentExpression = node => {
 	return true;
 };
 
-/**
-@param {import('estree').Expression | import('estree').PrivateIdentifier} node
-*/
-const getPropertyName = node => {
-	if (node.type === 'Identifier') {
-		return node.name;
-	}
-
-	if (node.type === 'Literal') {
-		return `[${node.raw}]`;
-	}
-
-	if (
-		node.type === 'TemplateLiteral'
-		&& node.expressions.length === 0
-		&& node.quasis.length === 1
-	) {
-		return `[\`${node.quasis[0].value.raw}\`]`;
-	}
-};
-
 /**
 @param {import('eslint').Rule.Node} node
 @param {import('eslint').Rule.RuleContext['sourceCode']} sourceCode
@@ -67,6 +46,58 @@ const removeFieldAssignment = (node, sourceCode, fixer) => {
 		: fixer.remove(node);
 };
 
+/**
+@param {string} propertyName
+@param {import('estree').ClassBody} classBody
+*/
+const findClassFieldNamed = (propertyName, classBody) => {
+	for (const classBodyChild of classBody.body) {
+		if (
+			classBodyChild.type === 'PropertyDefinition'
+			&& classBodyChild.key.type === 'Identifier'
+			&& classBodyChild.key.name === propertyName
+		) {
+			return classBodyChild;
+		}
+	}
+};
+
+/**
+@param {string} propertyName
+@param {string} propertyValue
+@param {import('estree').ClassBody} classBody
+@param {import('estree').MethodDefinition} constructor
+@param {import('eslint').Rule.RuleContext['sourceCode']} sourceCode
+@param {import('eslint').Rule.RuleFixer} fixer
+*/
+const addOrReplaceClassFieldDeclaration = (
+	propertyName,
+	propertyValue,
+	classBody,
+	constructor,
+	sourceCode,
+	fixer,
+) => {
+	const alreadyExistingDeclaration = findClassFieldNamed(
+		propertyName,
+		classBody,
+	);
+
+	if (alreadyExistingDeclaration) {
+		return fixer.replaceText(
+			alreadyExistingDeclaration,
+			`${propertyName} = ${propertyValue}`,
+		);
+	}
+
+	const classBodyStartRange = [classBody.range[0], classBody.range[0] + 1];
+	const indent = getIndentString(constructor, sourceCode);
+	return fixer.insertTextAfterRange(
+		classBodyStartRange,
+		`\n${indent}${propertyName} = ${propertyValue};`,
+	);
+};
+
 /**
 @type {import('eslint').Rule.RuleModule['create']}
 */
@@ -87,39 +118,34 @@ const create = context => {
 				return;
 			}
 
-			const classBodyStartRange = [classBody.range[0], classBody.range[0] + 1];
-			const indent = getIndentString(constructor, sourceCode);
-
 			for (let i = constructorBody.length - 1; i >= 0; i--) {
 				const node = constructorBody[i];
 				if (
-					!isThisAssignmentExpression(node)
-					|| node.expression.right?.type !== 'Literal'
-					|| node.expression.operator !== '='
+					isThisAssignmentExpression(node)
+					&& node.expression.right?.type === 'Literal'
+					&& node.expression.operator === '='
+					&& node.expression.left.property.type === 'Identifier'
 				) {
-					continue;
+					return {
+						node,
+						messageId: MESSAGE_ID,
+
+						/**
+						@param {import('eslint').Rule.RuleFixer} fixer
+						*/
+						* fix(fixer) {
+							yield removeFieldAssignment(node, sourceCode, fixer);
+							yield addOrReplaceClassFieldDeclaration(
+								node.expression.left.property.name,
+								node.expression.right.raw,
+								classBody,
+								constructor,
+								sourceCode,
+								fixer,
+							);
+						},
+					};
 				}
-
-				const propertyName = getPropertyName(node.expression.left.property);
-				if (!propertyName) {
-					continue;
-				}
-
-				return {
-					node,
-					messageId: MESSAGE_ID,
-
-					/**
-      				@param {import('eslint').Rule.RuleFixer} fixer
-	    			*/
-					* fix(fixer) {
-						yield removeFieldAssignment(node, sourceCode, fixer);
-						yield fixer.insertTextAfterRange(
-							classBodyStartRange,
-							`\n${indent}${propertyName} = ${node.expression.right.raw};`,
-						);
-					},
-				};
 			}
 		},
 	};
diff --git a/test/prefer-class-fields.mjs b/test/prefer-class-fields.mjs
index 52beae2b7f..823e55919d 100644
--- a/test/prefer-class-fields.mjs
+++ b/test/prefer-class-fields.mjs
@@ -75,15 +75,9 @@ test.snapshot({
 		`,
 		outdent`
 			class Foo {
+				foo = 'test';
 				constructor() {
-					this['foo'] = 'foo';
-				}
-			}
-		`,
-		outdent`
-			class Foo {
-				constructor() {
-					this[\`foo\`] = 'foo';
+					this.foo = 'foo';
 				}
 			}
 		`,
diff --git a/test/snapshots/prefer-class-fields.mjs.md b/test/snapshots/prefer-class-fields.mjs.md
index d3b6e6ab0e..c21d297e0e 100644
--- a/test/snapshots/prefer-class-fields.mjs.md
+++ b/test/snapshots/prefer-class-fields.mjs.md
@@ -148,56 +148,24 @@ Generated by [AVA](https://avajs.dev).
       6 | }␊
     `
 
-## invalid(5): class Foo { constructor() { this['foo'] = 'foo'; } }
+## invalid(5): class Foo { foo = 'test'; constructor() { this.foo = 'foo'; } }
 
 > Input
 
     `␊
       1 | class Foo {␊
-      2 | 	constructor() {␊
-      3 | 		this['foo'] = 'foo';␊
-      4 | 	}␊
-      5 | }␊
-    `
-
-> Output
-
-    `␊
-      1 | class Foo {␊
-      2 | 	['foo'] = 'foo';␊
+      2 | 	foo = 'test';␊
       3 | 	constructor() {␊
-      4 | 	}␊
-      5 | }␊
-    `
-
-> Error 1/1
-
-    `␊
-      1 | class Foo {␊
-      2 | 	constructor() {␊
-    > 3 | 		this['foo'] = 'foo';␊
-        | 		^^^^^^^^^^^^^^^^^^^^ Prefer class field declaration over \`this\` assignment in constructor for static values.␊
-      4 | 	}␊
-      5 | }␊
-    `
-
-## invalid(6): class Foo { constructor() { this[`foo`] = 'foo'; } }
-
-> Input
-
-    `␊
-      1 | class Foo {␊
-      2 | 	constructor() {␊
-      3 | 		this[\`foo\`] = 'foo';␊
-      4 | 	}␊
-      5 | }␊
+      4 | 		this.foo = 'foo';␊
+      5 | 	}␊
+      6 | }␊
     `
 
 > Output
 
     `␊
       1 | class Foo {␊
-      2 | 	[\`foo\`] = 'foo';␊
+      2 | 	foo = 'foo'␊
       3 | 	constructor() {␊
       4 | 	}␊
       5 | }␊
@@ -207,9 +175,10 @@ Generated by [AVA](https://avajs.dev).
 
     `␊
       1 | class Foo {␊
-      2 | 	constructor() {␊
-    > 3 | 		this[\`foo\`] = 'foo';␊
-        | 		^^^^^^^^^^^^^^^^^^^^ Prefer class field declaration over \`this\` assignment in constructor for static values.␊
-      4 | 	}␊
-      5 | }␊
+      2 | 	foo = 'test';␊
+      3 | 	constructor() {␊
+    > 4 | 		this.foo = 'foo';␊
+        | 		^^^^^^^^^^^^^^^^^ Prefer class field declaration over \`this\` assignment in constructor for static values.␊
+      5 | 	}␊
+      6 | }␊
     `
diff --git a/test/snapshots/prefer-class-fields.mjs.snap b/test/snapshots/prefer-class-fields.mjs.snap
index fa6d236595b0f1ead9f1fab31ea1fadaa3cfb661..445d2abffe984f19b39ed030016b2d0963a8766c 100644
GIT binary patch
literal 706
zcmV;z0zLgfRzV<BZeeh9Xm4~Nb~6eC08og%D3Z;HL2u!d1mB^9nfJ}9uFAh)bM7%K
zBT@zrGarix00000000Bcmd$R{KoG~{B81{wB_3c@4rx`XC|@9fk{d_}mBImuN`Shx
z*XdHn8+O-GP!n-LJ#p=c6O;$wF?a(`Tsd*&0gzKW@z}d|0#w1bteu(v%=~6&K6!^e
zcaG)hIaN&gbkt$Nkoe5qtZ&@`$0t(4ea_(o93Ds|LPv42xdkVnj+or>IEN0@JkD!(
zVFD8-12T|DT*-Imu1geo=3J><t3;1=wX$wKwE^ldP8+rX8Zd@x#=Z^EjE<{0KQ=%s
zdNZ*B+AxNRO?`4mefl66gerFX0=eBYyUkc`>ZNEMdV8Uod;FI6xc0TOc%<EeNMZWs
zW%hx`f_hZM);&gj7hLN2L=eSz0DMRV97F~WfJn)DL7xT+SdcCwcwB%~L@@`3#1E<5
zF@?(R3Bd)_Z`Kn|o+O+!mgXcmX~ahj6FYBF5num9cB&c;amdryZ<)A~ND^I+tDL`<
zUc6QYrtKG^?Z*<dnRC-E%#DG>OJz};h&+p<gvDk7i$wIo$Z<K7$(OJVHASULy>7<;
zXqu4yg6i^d!MdchEy-?PYm&CAMsu9WX-aRK5dVxqI4cOjz&Li8V;l$DUMwW7Y}69_
z)(s^5y0wDbcMEgBiWbr)F5g1ONei`REwuaQ;ww5*G;k$c{K8Gur&5w0je1Ik13Ev5
zTP7fV3LV&pZEYC3<^!tSdyJexhpv`$IkQq`WZ^>Q<SjG<&XC&ErPS&?=5`JgM#~UJ
z`H<MR){)XR>k{+YEz7GB{{LcxJWTj+XGTbT3&eBa50~H(+8SP!-l(%{uV@|B-csfC
oK1W&}Ep)s8)nfb;LHNCVo)kx)-BMP&EtlZ+8<nlp+FuO-01sMDH~;_u

literal 726
zcmV;{0xA7LRzV<BZeeh9Xm4~Nb~6eC090$xc(<ubsnSWh8dfhLw~==&wD9Jk(z(Rt
zpgcH@mmiA=00000000Bcmd|d}KoG{`B81{wB_3c@4rzr{lz&A6CE`*f4yYi6)Cv`4
zYp>H)9dFoOM?p=*0l|f9Pn@7U0FS|mD<`hJ0S|zj+DXRVO`NDD%`IzZzHerJlbx^L
zk<XnI`SF}8rhM9Ou%JhL=5Cg^9)RN$Dd92aa0(6&q!OW{xY*o+Q&7iDZhM?V14<s}
zrH3$tA(H{=%44qN`*YVNitIZ#3bzW;$GTZqw_e%+Wf)8cwgD<IfMP1X4N#4aiy0jo
zpcXwD+5mMJz|f{XIify&5_Cfq%N`=xJ+o{oa#e3dE9mWoYNGgST5;`1A%CXL8JWW9
z$?Nn7o(bwv5l8nJ^<8kO;}by?;{os<70`+Twtz^<+Chf~3Rp1RM)0@*sfc0@^oSo)
zxot|7?FzvKl<$=jPM#;6R2JqWIjO`)6%#w}P!r!=B0EKmhdAX??mH%~B(g*o<0_+9
z)0@}Yz_k5EwEbCtHgj#7GizfY@k&|L79z`HKVh*tgGD0RVI(}C$>dGA3nfLRntEJ~
ze^E6d`yKV=OU}Mbd0UX(tk<M$MUCgUlB1H|HzEEFrEoSQ1q0()FvB=bww^B~t!*?C
z2i6^A{I<1%+Bav`eib96EnIelPLdI-jYsI|+l#koU(vvoaPbWfRfkGR+BBLe8FuO9
zARd{3bSN}nBaXFUn3~V1bDuDB1|Pa!PV9_ZnX-i&nX#Aa4md+@KP=={r<mC}P#QHu
z8uKrS18W^QU9+yRuFZLMHNt-_u8>Cw|MeW}%&XC#!r`3F*F&qq{&F{TS}ND_OOWyl
zv$7`o@(b{91l!Lg7hsJgGdZhYgU8(L<l&~}ao+kr+@z!~nVW3%m2;D|bRD_*2jpy4
I(r^y|0BV6!?*IS*


From 3a9c5f81f4b64c8ff5898b7ef14c1b57486b664d Mon Sep 17 00:00:00 2001
From: Jakub Freisler <jakub@frsource.org>
Date: Fri, 20 Dec 2024 03:02:01 +0100
Subject: [PATCH 12/15] chore: lint fix

---
 rules/prefer-class-fields.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rules/prefer-class-fields.js b/rules/prefer-class-fields.js
index 201e448467..f33cfc3c70 100644
--- a/rules/prefer-class-fields.js
+++ b/rules/prefer-class-fields.js
@@ -118,8 +118,8 @@ const create = context => {
 				return;
 			}
 
-			for (let i = constructorBody.length - 1; i >= 0; i--) {
-				const node = constructorBody[i];
+			for (let index = constructorBody.length - 1; index >= 0; index--) {
+				const node = constructorBody[index];
 				if (
 					isThisAssignmentExpression(node)
 					&& node.expression.right?.type === 'Literal'

From f9caf1b8fdf8f85b87c2036023b6bf2e7972e476 Mon Sep 17 00:00:00 2001
From: Jakub Freisler <jakub@frsource.org>
Date: Sat, 21 Dec 2024 13:53:02 +0100
Subject: [PATCH 13/15] feat: handle only non-computed properties

---
 rules/prefer-class-fields.js | 57 +++++++++++++++++++-----------------
 test/prefer-class-fields.mjs | 17 +++++++----
 2 files changed, 42 insertions(+), 32 deletions(-)

diff --git a/rules/prefer-class-fields.js b/rules/prefer-class-fields.js
index f33cfc3c70..b839b83241 100644
--- a/rules/prefer-class-fields.js
+++ b/rules/prefer-class-fields.js
@@ -1,26 +1,27 @@
-'use strict';
-const getIndentString = require('./utils/get-indent-string.js');
+"use strict";
+const getIndentString = require("./utils/get-indent-string.js");
 
-const MESSAGE_ID = 'prefer-class-fields/error';
+const MESSAGE_ID = "prefer-class-fields/error";
 const messages = {
-	[MESSAGE_ID]: 'Prefer class field declaration over `this` assignment in constructor for static values.',
+	[MESSAGE_ID]:
+		"Prefer class field declaration over `this` assignment in constructor for static values.",
 };
 
 /**
 @param {import('eslint').Rule.Node} node
 @returns {node is import('estree').ExpressionStatement & {expression: import('estree').AssignmentExpression & {left: import('estree').MemberExpression & {object: import('estree').ThisExpression}}}}
 */
-const isThisAssignmentExpression = node => {
+const isThisAssignmentExpression = (node) => {
 	if (
-		node.type !== 'ExpressionStatement'
-		|| node.expression.type !== 'AssignmentExpression'
+		node.type !== "ExpressionStatement" ||
+		node.expression.type !== "AssignmentExpression"
 	) {
 		return false;
 	}
 
 	const lhs = node.expression.left;
 
-	if (!lhs.object || lhs.object.type !== 'ThisExpression') {
+	if (!lhs.object || lhs.object.type !== "ThisExpression") {
 		return false;
 	}
 
@@ -33,16 +34,16 @@ const isThisAssignmentExpression = node => {
 @param {import('eslint').Rule.RuleFixer} fixer
 */
 const removeFieldAssignment = (node, sourceCode, fixer) => {
-	const {line} = node.loc.start;
+	const { line } = node.loc.start;
 	const nodeText = sourceCode.getText(node);
 	const lineText = sourceCode.lines[line - 1];
 	const isOnlyNodeOnLine = lineText.trim() === nodeText;
 
 	return isOnlyNodeOnLine
 		? fixer.removeRange([
-			sourceCode.getIndexFromLoc({line, column: 0}),
-			sourceCode.getIndexFromLoc({line: line + 1, column: 0}),
-		])
+				sourceCode.getIndexFromLoc({ line, column: 0 }),
+				sourceCode.getIndexFromLoc({ line: line + 1, column: 0 }),
+			])
 		: fixer.remove(node);
 };
 
@@ -53,9 +54,9 @@ const removeFieldAssignment = (node, sourceCode, fixer) => {
 const findClassFieldNamed = (propertyName, classBody) => {
 	for (const classBodyChild of classBody.body) {
 		if (
-			classBodyChild.type === 'PropertyDefinition'
-			&& classBodyChild.key.type === 'Identifier'
-			&& classBodyChild.key.name === propertyName
+			classBodyChild.type === "PropertyDefinition" &&
+			classBodyChild.key.type === "Identifier" &&
+			classBodyChild.key.name === propertyName
 		) {
 			return classBodyChild;
 		}
@@ -101,14 +102,14 @@ const addOrReplaceClassFieldDeclaration = (
 /**
 @type {import('eslint').Rule.RuleModule['create']}
 */
-const create = context => {
-	const {sourceCode} = context;
+const create = (context) => {
+	const { sourceCode } = context;
 
 	return {
 		ClassBody(classBody) {
-			const constructor = classBody.body.find(x => x.kind === 'constructor');
+			const constructor = classBody.body.find((x) => x.kind === "constructor");
 
-			if (!constructor || constructor.type !== 'MethodDefinition') {
+			if (!constructor || constructor.type !== "MethodDefinition") {
 				return;
 			}
 
@@ -121,10 +122,11 @@ const create = context => {
 			for (let index = constructorBody.length - 1; index >= 0; index--) {
 				const node = constructorBody[index];
 				if (
-					isThisAssignmentExpression(node)
-					&& node.expression.right?.type === 'Literal'
-					&& node.expression.operator === '='
-					&& node.expression.left.property.type === 'Identifier'
+					isThisAssignmentExpression(node) &&
+					node.expression.right?.type === "Literal" &&
+					node.expression.operator === "=" &&
+					node.expression.left.property.type === "Identifier" &&
+					!node.expression.left.computed
 				) {
 					return {
 						node,
@@ -133,7 +135,7 @@ const create = context => {
 						/**
 						@param {import('eslint').Rule.RuleFixer} fixer
 						*/
-						* fix(fixer) {
+						*fix(fixer) {
 							yield removeFieldAssignment(node, sourceCode, fixer);
 							yield addOrReplaceClassFieldDeclaration(
 								node.expression.left.property.name,
@@ -155,12 +157,13 @@ const create = context => {
 module.exports = {
 	create,
 	meta: {
-		type: 'suggestion',
+		type: "suggestion",
 		docs: {
-			description: 'Prefer class field declarations over assigning static values in constructor using `this`.',
+			description:
+				"Prefer class field declarations over assigning static values in constructor using `this`.",
 			recommended: true,
 		},
-		fixable: 'code',
+		fixable: "code",
 		hasSuggestions: false,
 		messages,
 	},
diff --git a/test/prefer-class-fields.mjs b/test/prefer-class-fields.mjs
index 823e55919d..a96585ad2c 100644
--- a/test/prefer-class-fields.mjs
+++ b/test/prefer-class-fields.mjs
@@ -1,9 +1,9 @@
-import outdent from 'outdent';
-import {getTester} from './utils/test.mjs';
+import outdent from "outdent";
+import { getTester } from "./utils/test.mjs";
 
-const {test} = getTester(import.meta);
+const { test } = getTester(import.meta);
 
-const MESSAGE_ID = 'prefer-class-fields/error';
+const MESSAGE_ID = "prefer-class-fields/error";
 
 test.snapshot({
 	valid: [
@@ -31,6 +31,13 @@ test.snapshot({
 				}
 			}
 		`,
+		outdent`
+			class Foo {
+				constructor() {
+					this[foo] = 'foo';
+				}
+			}
+		`,
 		outdent`
 			class Foo {
 				something = 'a';
@@ -107,7 +114,7 @@ test.typescript({
 					}
 				}
 			`,
-			errors: [{messageId: MESSAGE_ID}],
+			errors: [{ messageId: MESSAGE_ID }],
 			output: outdent`
 				class MyError extends Error {
 					name = "MyError";

From 3376845a24b906cc6d5fec99524b99570397136c Mon Sep 17 00:00:00 2001
From: Jakub Freisler <jakub@frsource.org>
Date: Sun, 22 Dec 2024 18:53:16 +0100
Subject: [PATCH 14/15] chore: stop static analysis on unsupported cases

---
 rules/prefer-class-fields.js | 72 +++++++++++++++++++++---------------
 test/prefer-class-fields.mjs | 18 ++++++---
 2 files changed, 55 insertions(+), 35 deletions(-)

diff --git a/rules/prefer-class-fields.js b/rules/prefer-class-fields.js
index b839b83241..2c90a46c81 100644
--- a/rules/prefer-class-fields.js
+++ b/rules/prefer-class-fields.js
@@ -1,27 +1,27 @@
-"use strict";
-const getIndentString = require("./utils/get-indent-string.js");
+'use strict';
+const getIndentString = require('./utils/get-indent-string.js');
 
-const MESSAGE_ID = "prefer-class-fields/error";
+const MESSAGE_ID = 'prefer-class-fields/error';
 const messages = {
 	[MESSAGE_ID]:
-		"Prefer class field declaration over `this` assignment in constructor for static values.",
+		'Prefer class field declaration over `this` assignment in constructor for static values.',
 };
 
 /**
 @param {import('eslint').Rule.Node} node
 @returns {node is import('estree').ExpressionStatement & {expression: import('estree').AssignmentExpression & {left: import('estree').MemberExpression & {object: import('estree').ThisExpression}}}}
 */
-const isThisAssignmentExpression = (node) => {
+const isThisAssignmentExpression = node => {
 	if (
-		node.type !== "ExpressionStatement" ||
-		node.expression.type !== "AssignmentExpression"
+		node.type !== 'ExpressionStatement'
+		|| node.expression.type !== 'AssignmentExpression'
 	) {
 		return false;
 	}
 
 	const lhs = node.expression.left;
 
-	if (!lhs.object || lhs.object.type !== "ThisExpression") {
+	if (!lhs.object || lhs.object.type !== 'ThisExpression') {
 		return false;
 	}
 
@@ -34,16 +34,16 @@ const isThisAssignmentExpression = (node) => {
 @param {import('eslint').Rule.RuleFixer} fixer
 */
 const removeFieldAssignment = (node, sourceCode, fixer) => {
-	const { line } = node.loc.start;
+	const {line} = node.loc.start;
 	const nodeText = sourceCode.getText(node);
 	const lineText = sourceCode.lines[line - 1];
 	const isOnlyNodeOnLine = lineText.trim() === nodeText;
 
 	return isOnlyNodeOnLine
 		? fixer.removeRange([
-				sourceCode.getIndexFromLoc({ line, column: 0 }),
-				sourceCode.getIndexFromLoc({ line: line + 1, column: 0 }),
-			])
+			sourceCode.getIndexFromLoc({line, column: 0}),
+			sourceCode.getIndexFromLoc({line: line + 1, column: 0}),
+		])
 		: fixer.remove(node);
 };
 
@@ -54,9 +54,9 @@ const removeFieldAssignment = (node, sourceCode, fixer) => {
 const findClassFieldNamed = (propertyName, classBody) => {
 	for (const classBodyChild of classBody.body) {
 		if (
-			classBodyChild.type === "PropertyDefinition" &&
-			classBodyChild.key.type === "Identifier" &&
-			classBodyChild.key.name === propertyName
+			classBodyChild.type === 'PropertyDefinition'
+			&& classBodyChild.key.type === 'Identifier'
+			&& classBodyChild.key.name === propertyName
 		) {
 			return classBodyChild;
 		}
@@ -102,14 +102,14 @@ const addOrReplaceClassFieldDeclaration = (
 /**
 @type {import('eslint').Rule.RuleModule['create']}
 */
-const create = (context) => {
-	const { sourceCode } = context;
+const create = context => {
+	const {sourceCode} = context;
 
 	return {
 		ClassBody(classBody) {
-			const constructor = classBody.body.find((x) => x.kind === "constructor");
+			const constructor = classBody.body.find(x => x.kind === 'constructor');
 
-			if (!constructor || constructor.type !== "MethodDefinition") {
+			if (!constructor || constructor.type !== 'MethodDefinition') {
 				return;
 			}
 
@@ -119,14 +119,26 @@ const create = (context) => {
 				return;
 			}
 
-			for (let index = constructorBody.length - 1; index >= 0; index--) {
-				const node = constructorBody[index];
+			const firstInvalidProperty = constructorBody.findIndex(
+				node => node.type !== 'ExpressionStatement',
+			);
+			const validConstructorProperties
+				= firstInvalidProperty === -1
+					? constructorBody
+					: constructorBody.slice(0, firstInvalidProperty);
+
+			for (
+				let index = validConstructorProperties.length - 1;
+				index >= 0;
+				index--
+			) {
+				const node = validConstructorProperties[index];
 				if (
-					isThisAssignmentExpression(node) &&
-					node.expression.right?.type === "Literal" &&
-					node.expression.operator === "=" &&
-					node.expression.left.property.type === "Identifier" &&
-					!node.expression.left.computed
+					isThisAssignmentExpression(node)
+					&& node.expression.right?.type === 'Literal'
+					&& node.expression.operator === '='
+					&& node.expression.left.property.type === 'Identifier'
+					&& !node.expression.left.computed
 				) {
 					return {
 						node,
@@ -135,7 +147,7 @@ const create = (context) => {
 						/**
 						@param {import('eslint').Rule.RuleFixer} fixer
 						*/
-						*fix(fixer) {
+						* fix(fixer) {
 							yield removeFieldAssignment(node, sourceCode, fixer);
 							yield addOrReplaceClassFieldDeclaration(
 								node.expression.left.property.name,
@@ -157,13 +169,13 @@ const create = (context) => {
 module.exports = {
 	create,
 	meta: {
-		type: "suggestion",
+		type: 'suggestion',
 		docs: {
 			description:
-				"Prefer class field declarations over assigning static values in constructor using `this`.",
+				'Prefer class field declarations over assigning static values in constructor using `this`.',
 			recommended: true,
 		},
-		fixable: "code",
+		fixable: 'code',
 		hasSuggestions: false,
 		messages,
 	},
diff --git a/test/prefer-class-fields.mjs b/test/prefer-class-fields.mjs
index a96585ad2c..dfe06842ba 100644
--- a/test/prefer-class-fields.mjs
+++ b/test/prefer-class-fields.mjs
@@ -1,9 +1,9 @@
-import outdent from "outdent";
-import { getTester } from "./utils/test.mjs";
+import outdent from 'outdent';
+import {getTester} from './utils/test.mjs';
 
-const { test } = getTester(import.meta);
+const {test} = getTester(import.meta);
 
-const MESSAGE_ID = "prefer-class-fields/error";
+const MESSAGE_ID = 'prefer-class-fields/error';
 
 test.snapshot({
 	valid: [
@@ -46,6 +46,14 @@ test.snapshot({
 				}
 			}
 		`,
+		outdent`
+			class Foo {
+				constructor() {
+					if (something) { return; }
+					this.elo = 'foo';
+				}
+			}
+		`,
 	],
 	invalid: [
 		outdent`
@@ -114,7 +122,7 @@ test.typescript({
 					}
 				}
 			`,
-			errors: [{ messageId: MESSAGE_ID }],
+			errors: [{messageId: MESSAGE_ID}],
 			output: outdent`
 				class MyError extends Error {
 					name = "MyError";

From d9078277b8e50b26459148bc1fddb09ce03fec84 Mon Sep 17 00:00:00 2001
From: Jakub Freisler <jakub@frsource.org>
Date: Wed, 25 Dec 2024 13:39:21 +0100
Subject: [PATCH 15/15] chore: add missing semicolon

---
 rules/prefer-class-fields.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/rules/prefer-class-fields.js b/rules/prefer-class-fields.js
index 2c90a46c81..74c332354a 100644
--- a/rules/prefer-class-fields.js
+++ b/rules/prefer-class-fields.js
@@ -87,7 +87,7 @@ const addOrReplaceClassFieldDeclaration = (
 	if (alreadyExistingDeclaration) {
 		return fixer.replaceText(
 			alreadyExistingDeclaration,
-			`${propertyName} = ${propertyValue}`,
+			`${propertyName} = ${propertyValue};`,
 		);
 	}