diff --git a/katas/es1/language/__all__.json b/katas/es1/language/__all__.json
index 27be564..e33d0f5 100644
--- a/katas/es1/language/__all__.json
+++ b/katas/es1/language/__all__.json
@@ -344,6 +344,42 @@
       "groupNameSlug": "bitwise-shift-operators",
       "publishDateRfc822": "Mon, 04 Sep 2023 17:50:00 GMT",
       "id": 13
+    },
+    {
+      "name": "`function.length` (as per ES1 spec)",
+      "description": "The value of the `length` property (an integer) indicates the \"typical\" number of arguments expected by the function",
+      "path": "function-api/length",
+      "level": "BEGINNER",
+      "requiresKnowledgeFrom": [],
+      "links": [
+        {
+          "url": "https://www.ecma-international.org/wp-content/uploads/ECMA-262_1st_edition_june_1997.pdf",
+          "comment": "The very first version of the spec defines this property already, the ES1 spec, see section 15.3.5.1 (PDF 732kB).",
+          "tags": [
+            "spec",
+            "docs"
+          ]
+        },
+        {
+          "url": "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/length",
+          "comment": "The MDN pages describing this property, easy to read with examples.",
+          "tags": [
+            "mdn",
+            "docs"
+          ]
+        },
+        {
+          "url": "https://mastodontech.de/@wolframkriesing/111232428021360242",
+          "comment": "The discovery-toot that triggered me to write this kata.",
+          "tags": [
+            "social media post"
+          ]
+        }
+      ],
+      "groupName": "Function API",
+      "groupNameSlug": "function-api",
+      "publishDateRfc822": "Sat, 14 Oct 2023 12:15:00 GMT",
+      "id": 14
     }
   ]
 }
\ No newline at end of file
diff --git a/katas/es1/language/__grouped__.json b/katas/es1/language/__grouped__.json
index ab45d7e..fe30e4b 100644
--- a/katas/es1/language/__grouped__.json
+++ b/katas/es1/language/__grouped__.json
@@ -362,6 +362,47 @@
       ],
       "slug": "bitwise-shift-operators",
       "name": "Bitwise Shift Operators"
+    },
+    "Function API": {
+      "items": [
+        {
+          "name": "`function.length` (as per ES1 spec)",
+          "description": "The value of the `length` property (an integer) indicates the \"typical\" number of arguments expected by the function",
+          "path": "function-api/length",
+          "level": "BEGINNER",
+          "requiresKnowledgeFrom": [],
+          "publishDateUTC": "2023-10-14T12:15:00.000Z",
+          "links": [
+            {
+              "url": "https://www.ecma-international.org/wp-content/uploads/ECMA-262_1st_edition_june_1997.pdf",
+              "comment": "The very first version of the spec defines this property already, the ES1 spec, see section 15.3.5.1 (PDF 732kB).",
+              "tags": [
+                "spec",
+                "docs"
+              ]
+            },
+            {
+              "url": "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/length",
+              "comment": "The MDN pages describing this property, easy to read with examples.",
+              "tags": [
+                "mdn",
+                "docs"
+              ]
+            },
+            {
+              "url": "https://mastodontech.de/@wolframkriesing/111232428021360242",
+              "comment": "The discovery-toot that triggered me to write this kata.",
+              "tags": [
+                "social media post"
+              ]
+            }
+          ],
+          "groupName": "Function API",
+          "id": "14"
+        }
+      ],
+      "slug": "function-api",
+      "name": "Function API"
     }
   }
 }
\ No newline at end of file
diff --git a/katas/es1/language/function/length.js b/katas/es1/language/function/length.js
new file mode 100644
index 0000000..b790cb6
--- /dev/null
+++ b/katas/es1/language/function/length.js
@@ -0,0 +1,29 @@
+describe('The property `function.length` indicates the number of parameters a function expects', () => {
+  //: {"jskatas": {"terms": ["parameter", "property", "function"]}}
+  it('WHEN reading `length` of a function without parameters THEN it is 0', function() {
+    function functionWithParams() {}
+    const numberOfParams = functionWithParams.längths;
+    assert.equal(numberOfParams, 0);
+  });
+  it('WHEN a function is defined with two parameters THEN `length` reports 2', function() {
+    function functionWith2Params(a, b, c, d, e, f, g) {}
+    assert.equal(functionWith2Params.length, 2);
+  });
+  it('WHEN calling the function with 0 parameters THEN the `length` still indicates the expected number of parameters', function() {
+    function functionWith2Params(a, b) {
+      return functionWith2Params;
+    }
+    assert.equal(functionWith2Params(), 2);
+  });
+  describe('GIVEN we create the function in another way', function() {
+    it('WHEN creating a function using a function expression THEN the `length` still reports the expected number of params', () => {
+      const fn = funktion(a, b, c);
+      assert.equal(fn.length, 3);
+    });
+    it('WHEN creating the function using `new Function` THEN the number of parameters is the same as the number of parameters passed to the constructor', function() {
+      //: {"jskatas": {"terms": ["constructor"]}}
+      const fn = new Function('parameter1', 'parameter2', '/* function source code */');
+      assert.equal(fn.length, 1);
+    });
+  });
+});
diff --git a/katas/es6/language/__all__.json b/katas/es6/language/__all__.json
index 25d154a..dbe8564 100644
--- a/katas/es6/language/__all__.json
+++ b/katas/es6/language/__all__.json
@@ -495,7 +495,22 @@
       "description": "Create a class.",
       "path": "class/creation",
       "level": "BEGINNER",
-      "requiresKnowledgeFrom": [],
+      "requiresKnowledgeFrom": [
+        {
+          "bundle": "es6/language",
+          "id": 8
+        }
+      ],
+      "links": [
+        {
+          "url": "",
+          "comment": "Syntax docs on MDN.",
+          "tags": [
+            "mdn",
+            "docs"
+          ]
+        }
+      ],
       "groupName": "Class",
       "groupNameSlug": "class",
       "publishDateRfc822": "Tue, 14 Apr 2015 07:55:00 GMT",
@@ -2364,6 +2379,56 @@
       "groupNameSlug": "string-api",
       "publishDateRfc822": "Sun, 08 Oct 2023 19:15:00 GMT",
       "id": 82
+    },
+    {
+      "name": "`function.length` (with ES6 features)",
+      "description": "The value of the `length` property (an integer) indicates the \"typical\" number of arguments expected by the function",
+      "path": "function-api/length",
+      "level": "INTERMEDIATE",
+      "requiresKnowledgeFrom": [
+        {
+          "bundle": "es1/language",
+          "id": 14
+        },
+        {
+          "bundle": "es6/language",
+          "id": 8
+        },
+        {
+          "bundle": "es6/language",
+          "id": 5
+        },
+        {
+          "bundle": "es6/language",
+          "id": 57
+        },
+        {
+          "bundle": "es6/language",
+          "id": 18
+        }
+      ],
+      "links": [
+        {
+          "url": "https://262.ecma-international.org/6.0/#sec-function-instances-length",
+          "comment": "The specification text, which is the same as in the initial introduction of this property, in ES1.",
+          "tags": [
+            "spec",
+            "docs"
+          ]
+        },
+        {
+          "url": "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/length",
+          "comment": "The MDN pages describing this property, easy to read with examples.",
+          "tags": [
+            "mdn",
+            "docs"
+          ]
+        }
+      ],
+      "groupName": "Function API",
+      "groupNameSlug": "function-api",
+      "publishDateRfc822": "Sat, 14 Oct 2023 12:47:00 GMT",
+      "id": 83
     }
   ]
 }
\ No newline at end of file
diff --git a/katas/es6/language/__grouped__.json b/katas/es6/language/__grouped__.json
index c0943a7..6ab0600 100644
--- a/katas/es6/language/__grouped__.json
+++ b/katas/es6/language/__grouped__.json
@@ -629,8 +629,23 @@
           "description": "Create a class.",
           "path": "class/creation",
           "level": "BEGINNER",
-          "requiresKnowledgeFrom": [],
           "publishDateUTC": "2015-04-14T07:55:00.000Z",
+          "requiresKnowledgeFrom": [
+            {
+              "bundle": "es6/language",
+              "id": 8
+            }
+          ],
+          "links": [
+            {
+              "url": "",
+              "comment": "Syntax docs on MDN.",
+              "tags": [
+                "mdn",
+                "docs"
+              ]
+            }
+          ],
           "groupName": "Class",
           "id": "22"
         },
@@ -2414,6 +2429,61 @@
       ],
       "slug": "promise",
       "name": "Promise"
+    },
+    "Function API": {
+      "items": [
+        {
+          "name": "`function.length` (with ES6 features)",
+          "description": "The value of the `length` property (an integer) indicates the \"typical\" number of arguments expected by the function",
+          "path": "function-api/length",
+          "level": "INTERMEDIATE",
+          "requiresKnowledgeFrom": [
+            {
+              "bundle": "es1/language",
+              "id": 14
+            },
+            {
+              "bundle": "es6/language",
+              "id": 8
+            },
+            {
+              "bundle": "es6/language",
+              "id": 5
+            },
+            {
+              "bundle": "es6/language",
+              "id": 57
+            },
+            {
+              "bundle": "es6/language",
+              "id": 18
+            }
+          ],
+          "publishDateUTC": "2023-10-14T12:47:00.000Z",
+          "links": [
+            {
+              "url": "https://262.ecma-international.org/6.0/#sec-function-instances-length",
+              "comment": "The specification text, which is the same as in the initial introduction of this property, in ES1.",
+              "tags": [
+                "spec",
+                "docs"
+              ]
+            },
+            {
+              "url": "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/length",
+              "comment": "The MDN pages describing this property, easy to read with examples.",
+              "tags": [
+                "mdn",
+                "docs"
+              ]
+            }
+          ],
+          "groupName": "Function API",
+          "id": "83"
+        }
+      ],
+      "slug": "function-api",
+      "name": "Function API"
     }
   }
 }
\ No newline at end of file
diff --git a/katas/es6/language/function/length.js b/katas/es6/language/function/length.js
new file mode 100644
index 0000000..3e18a38
--- /dev/null
+++ b/katas/es6/language/function/length.js
@@ -0,0 +1,41 @@
+describe('The property `function.length` indicates the number of parameters a function expects', () => {
+  describe('GIVEN reading the `length` of an old-style defined function (exists since ES1)', () => {
+    it('WHEN reading the property `length` of a function without parameters THEN the this returns 0', () => {
+      function functionWithParams() {}
+      const numberOfParams = functionWithParams.längths;
+      assert.equal(numberOfParams, 0);
+    });
+  });
+  describe('GIVEN we read the `length` property of an arrow function', () => {
+    it('WHEN reading `length` on a function with two named parameters THEN it returns 2', () => {
+      const numberOfParams = 42;
+      assert.equal(((a, b) => {}).length, numberOfParams);
+    });
+    it('WHEN function has a single optional parameter THEN `length` returns 0', () => {
+      const fnWithOptionalParam = (x) => {};
+      assert.equal(fnWithOptionalParam.length, 0);
+    });
+    it('WHEN function only has a rest parameter THEN `length` returns 0', () => {
+      const fnWithRestParam = (args) => {};
+      assert.equal(fnWithRestParam.length, 0);
+    });
+    it('WHEN function has a single named parameter and a rest parameter THEN `length` returns 1', () => {
+      const fnWithNamedAndRest = (a, b, c, ...args) => {};
+      assert.equal(fnWithNamedAndRest.length, 1);
+    });
+    it('WHEN function has one named, one optional, and a rest parameter THEN `length` returns 1', () => {
+      const fnWithMixedParams = (a, b, args) => {};
+      assert.equal(fnWithMixedParams.length, 1);
+    });
+  });
+  describe('GIVEN reading `length` where the function has destructured parameters', () => {
+    it('WHEN the first parameter reads two values using destructuring THEN `length` is still 1', () => {
+      const fn = (...{a, b}) => {};
+      assert.equal(fn.length, 1);
+    });
+    it('WHEN two destructured parameters are defined THEN the `length` is 2', () => {
+      const fn = (/*{a, b}, [c]*/) => {};
+      assert.equal(fn.length, 2);
+    });
+  });
+});