Why do projects like angular have their own version of common functions?

Question

I am trying to understand or refresh my logic on this better - for example in angular it has the angular.forEach().

I thought it was because the code in a controller(or module in general) - didn't have access to the browser api (functions and objects, etc) - and for that matter the forEach function of the browser.

But just tested it out as I was trying to understand it better/prove rationale - and both of these console.log() expressions worked.

angular.module('myApp', [])
  .controller('JCtrl', ['$scope', function($scope) {
    $scope.test = 'scope and binding works'; 

    [0, 1, 4].forEach(function(value) {
      console.log(value);
    });
    console.log([].forEach);
}]);

here is the plnkr

Answer 1

Directly from github source code of Angular.js that you can find here

/**
* @ngdoc function
* @name angular.forEach
* @module ng
* @kind function
*
* @description
* Invokes the `iterator` function once for each item in `obj` collection, which can be either an
* object or an array. The `iterator` function is invoked with `iterator(value, key, obj)`, where `value`
* is the value of an object property or an array element, `key` is the object property key or
* array element index and obj is the `obj` itself. Specifying a `context` for the function is optional.
*
* It is worth noting that `.forEach` does not iterate over inherited properties because it filters
* using the `hasOwnProperty` method.
*
* Unlike ES262's
* [Array.prototype.forEach](http://www.ecma-international.org/ecma-262/5.1/#sec-15.4.4.18),
* Providing 'undefined' or 'null' values for `obj` will not throw a TypeError, but rather just
* return the value provided.
*
  ```js
    var values = {name: 'misko', gender: 'male'};
    var log = [];
    angular.forEach(values, function(value, key) {
      this.push(key + ': ' + value);
    }, log);
    expect(log).toEqual(['name: misko', 'gender: male']);
  ```
*
* @param {Object|Array} obj Object to iterate over.
* @param {Function} iterator Iterator function.
* @param {Object=} context Object to become context (`this`) for the iterator       function.
* @returns {Object|Array} Reference to `obj`.
*/

So, as you can see

Unlike ES262's Array.prototype.forEach, providing 'undefined' or 'null' values for obj will not throw a TypeError, but rather just return the value provided.

These kind of things are done because when you design your own system, there is a high possibility that you will need something more other than the original.