Array#keys (as implemented in ES 6)

README.md

@@ -56,6 +56,7 @@ It's about properties introduced with ES6 and those that have been updated in ne
 - `Array.prototype.filter` -> `require('es5-ext/array/#/filter')`
 - `Array.prototype.find` -> `require('es5-ext/array/#/find')`
 - `Array.prototype.findIndex` -> `require('es5-ext/array/#/find-index')`
+- `Array.prototype.keys` -> `require('es5-ext/array/#/keys')`
 - `Array.prototype.map` -> `require('es5-ext/array/#/map')`
 - `Array.prototype.slice` -> `require('es5-ext/array/#/slice')`
 - `Array.prototype.splice` -> `require('es5-ext/array/#/splice')`
@@ -287,6 +288,11 @@ Returns true if both context and _other_ lists have same content
 
 Returns true if all values in array are unique
 
+#### arr.keys() _(es5-ext/array/#/keys)_
+
+[_Introduced with ECMAScript 6_](http://people.mozilla.org/~jorendorff/es6-draft.html#sec-array.keys).  
+Return iterator object, where each iterated value represents array index.
+
 #### arr.last() _(es5-ext/array/#/last)_
 
 Returns value of last defined index

array/#/index.js

@@ -20,6 +20,7 @@ module.exports = {
 	firstIndex:     require('./first-index'),
 	flatten:        require('./flatten'),
 	forEachRight:   require('./for-each-right'),
+	keys:           require('./keys'),
 	group:          require('./group'),
 	indexesOf:      require('./indexes-of'),
 	intersection:   require('./intersection'),

array/#/keys/implement.js

@@ -0,0 +1,6 @@
+'use strict';
+
+if (!require('./is-implemented')()) {
+	Object.defineProperty(Array.prototype, 'keys', { value: require('./shim'),
+		configurable: true, enumerable: false, writable: true });
+}

array/#/keys/index.js

@@ -0,0 +1,4 @@
+'use strict';
+
+module.exports = require('./is-implemented')() ?
+		Array.prototype.keys : require('./shim');

array/#/keys/is-implemented.js

@@ -0,0 +1,14 @@
+'use strict';
+
+module.exports = function () {
+	var arr = [1, 'foo'], iterator, result;
+	if (typeof arr.keys !== 'function') return false;
+	iterator = arr.keys();
+	if (!iterator) return false;
+	if (typeof iterator.next !== 'function') return false;
+	result = iterator.next();
+	if (!result) return false;
+	if (result.value !== 0) return false;
+	if (result.done !== false) return false;
+	return true;
+};

array/#/keys/shim.js

@@ -0,0 +1,4 @@
+'use strict';
+
+var ArrayIterator = require('es6-iterator/array');
+module.exports = function () { return new ArrayIterator(this, 'key'); };

test/array/#/keys/implement.js

@@ -0,0 +1,5 @@
+'use strict';
+
+var isImplemented = require('../../../../array/#/keys/is-implemented');
+
+module.exports = function (a) { a(isImplemented(), true); };

test/array/#/keys/index.js

@@ -0,0 +1,3 @@
+'use strict';
+
+module.exports = require('./shim');

test/array/#/keys/is-implemented.js

@@ -0,0 +1,3 @@
+'use strict';
+
+module.exports = function (t, a) { a(typeof t(), 'boolean'); };

test/array/#/keys/shim.js

@@ -0,0 +1,9 @@
+'use strict';
+
+exports.__generic = function (t, a) {
+	var iterator = t.call(this);
+	a.deep(iterator.next(), { value: 0, done: false });
+	a.deep(iterator.next(), { value: 1, done: false });
+	a.deep(iterator.next(), { value: 2, done: false });
+	a.deep(iterator.next(), { value: undefined, done: true });
+};