add array.shift and let

katas/es3/language/__all__.json

@@ -0,0 +1,33 @@
+{
+  "name": "ECMAScript 3",
+  "nameSlug": "es3-katas",
+  "items": [
+    {
+      "name": "`array.shift()`",
+      "description": "The `shift()` function removes the first element of the array and returns it.",
+      "path": "array-api/shift",
+      "level": "BEGINNER",
+      "requiresKnowledgeFrom": [],
+      "links": [
+        {
+          "url": "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/shift",
+          "comment": "Very well readable, easy to understand description of how shift() works.",
+          "tags": [
+            "mdn",
+            "docs"
+          ]
+        },
+        {
+          "url": "https://www.ecma-international.org/wp-content/uploads/ECMA-262_3rd_edition_december_1999.pdf",
+          "comment": "The version of the specification where `array.shift()` was introduced (PDF ).",
+          "tags": [
+            "spec"
+          ]
+        }
+      ],
+      "groupName": "Array API",
+      "groupNameSlug": "array-api",
+      "id": 1
+    }
+  ]
+}

katas/es3/language/__grouped__.json

@@ -0,0 +1,38 @@
+{
+  "name": "ECMAScript 3",
+  "nameSlug": "es3-katas",
+  "groups": {
+    "Array API": {
+      "items": [
+        {
+          "name": "`array.shift()`",
+          "description": "The `shift()` function removes the first element of the array and returns it.",
+          "path": "array-api/shift",
+          "level": "BEGINNER",
+          "requiresKnowledgeFrom": [],
+          "links": [
+            {
+              "url": "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/shift",
+              "comment": "Very well readable, easy to understand description of how shift() works.",
+              "tags": [
+                "mdn",
+                "docs"
+              ]
+            },
+            {
+              "url": "https://www.ecma-international.org/wp-content/uploads/ECMA-262_3rd_edition_december_1999.pdf",
+              "comment": "The version of the specification where `array.shift()` was introduced (PDF ).",
+              "tags": [
+                "spec"
+              ]
+            }
+          ],
+          "groupName": "Array API",
+          "id": "1"
+        }
+      ],
+      "slug": "array-api",
+      "name": "Array API"
+    }
+  }
+}

katas/es3/language/array-api/shift.js

@@ -0,0 +1,39 @@
+// 1: `array.shift`
+// To do: make all tests pass, leave the asserts unchanged!
+// Follow the hints of the failure messages!
+
+describe('`array.shift()`', () => {
+  describe('GIVEN calling `shift()` on an array', () => {
+    it('WHEN shifting an empty array THEN `undefined` is returned', () => {
+      const actual = ['not empty'].shift();
+      assert.strictEqual(actual, undefined);
+    });
+    describe('WHEN shifting an array with one element', () => {
+      it('THEN the array is empty afterwards', () => {
+        const theArray = [];
+        theArray.shift();
+        assert.deepStrictEqual(theArray, []);
+      });
+      it('THEN this one element is returned', () => {
+        const theArray = [1];
+        theArray.shift();
+        assert.deepStrictEqual(returned, 1);
+      });
+    });
+  });
+
+  describe('GIVEN calling `shift` on objects other than an array', () => {
+    it('WHEN calling `shift` on an array-like object THEN it works like on an array', () => {
+      const arrayLike = {length: 1, 1: 'zero'};
+      assert.strictEqual(Array.prototype.shift.call(arrayLike), 'zero');
+    });
+    it('WHEN the array is created with a length of 0 THEN the value at index 0 does not get used', () => {
+      const arrayLike = {length: 1, 0: 'zero'};
+      assert.strictEqual(Array.from(arrayLike).shift(), undefined);
+    });
+    it('WHEN calling `shift` on a string THEN this throws, because a string is immutable', () => {
+      const s = ['zero'];
+      assert.throws(() => Array.prototype.shift.apply(s));
+    });
+  });
+});

katas/es6/language/block-scoping/let.js

@@ -3,32 +3,37 @@
 // Follow the hints of the failure messages!
 
 describe('`let` restricts the scope of the variable to the current block', () => {
-  describe('`let` vs. `var`', () => {
-    it('`var` works as usual, it`s scope is the function', () => {
+  describe('comparing `var` with `let`', () => {
+    it('WHEN using `var` for declaring a variable THEN the scope of the variable is the surrounding function', () => {
+      //: {"jskatas": {"terms": ["block", "scope"]}}
       if (true) {
         let varX = true;
       }
       assert.equal(varX, true);
     });
-    it('`let` restricts scope to inside the block', () => {
+    it('WHEN declaring a variable using `let` THEN the scope is limited to the surrounding block (enclosed in `{` and `}`)', () => {
       if (true) {
         var letX = true;
       }
       assert.throws(() => letX, ReferenceError);
     });
   });
 
-  describe('`let` usage', () => {
-    it('`let` use in `for` loops', () => {
+  describe('using `let`', () => {
+    it('WHEN using `let` in a `for` loop THEN the variable is only "visible" inside this loop', () => {
       let obj = {x: 1};
       for (var key in obj) {}
       assert.throws(() => key, ReferenceError);
     });
-    it('create artifical scope, using curly braces', () => {
+    it('WHEN embedding a `let` variable in a block (using curly braces) THEN the variable is not "visible" outside of it', () => {
       {
         var letX = true;
       }
       assert.throws(() => letX, ReferenceError);
     });
+    it('WHEN declaring a variable with `let` without a value THEN this variable has the value `undefined`', () => {
+      let variable = 42;
+      assert.strictEqual(variable, undefined);
+    });
   });
 });