Merge branch 'pr/28'

map/README.md

@@ -0,0 +1,18 @@
+You might know about [map](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/map) method, let's implement your own `map` one and name it, say `_map`.
+
+`_map` should function like `map` does:
+
+```js
+require('./')() // <- this is the file you make;
+
+var numbers = [1, 2, 3];
+
+var doubles = numbers._map(function(number) {
+  return number * 2;
+});
+
+console.log(doubles); // [1, 4, 6]
+
+```
+
+More info: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/map

map/package.json

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+{
+  "private": true,
+  "scripts": {
+    "test": "node ../node_modules/mocha/bin/mocha"
+  }
+}

map/test.js

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+var assert = require('assert');
+
+var NativeMap = Array.prototype.map;
+var calledNativeMap;
+Array.prototype.map = function() {
+  calledNativeMap = true;
+  return NativeMap.apply(this, arguments);
+}
+
+var map = require('./');
+
+
+
+describe('map', function() {
+
+  it('should not use the native map', function() {
+    calledNativeMap = false;
+    ['x'].map(function(x) { return x; });
+    assert(!calledNativeMap);
+  });
+
+  it('should return another array', function() {
+    var arr = [1, 2, 3];
+    var mapped = map(arr, function() {});
+
+    assert.notEqual(arr, mapped);
+  });
+
+  it('should return the right results', function() {
+    var arr = [1, 2, 3];
+    var mapped = map(arr, function(value) {
+      return value * 2;
+    });
+
+    assert.deepEqual(mapped, [2, 4, 6]);
+  });
+
+  it('callback will be called once for each element', function() {
+    var called = 0;
+    var arr = [1, 2, 3];
+
+    map(function(value) {
+      called++;
+      return value;
+    });
+
+    assert.equal(called, 3);
+  });
+
+  it('callback will be invoked with three arguments', function() {
+    var args;
+    var arr = [1];
+
+    map(arr, function() {
+      args = arguments.length;
+    });
+
+    assert.equal(args, 3);
+  });
+
+  it("callback's arguments (value, index, array) should have right values", function() {
+    var i = 0;
+    var arr = [1, 2, 3];
+
+    map(arr, function(value, index, array) {
+      assert.equal(value, arr[i]);
+      assert.equal(index, i);
+      assert.deepEqual(arr, array);
+      i++;
+    });
+  });
+
+  it('callback should gets called with context', function() {
+    var ctx;
+    var arr = [5];
+
+    map(arr, function() {
+      ctx = this;
+    }, 3);
+
+    assert.equal(ctx, 3);
+  });
+});