myForEach.html

<script src="..\my-jsArrayMethods\simpletest.js"></script>
<script>
	// my version of the native forEach method.
	// does not overwrite Array.prototype.forEach.
	
	function myForEach(originalArray, callback, optionalThisObject) {
		// var boundCallback = callback;
		if (optionalThisObject) {
			// boundCallback = callback.bind(optionalThisObject);
			callback = callback.bind(optionalThisObject);
		};
		for (var i = 0; i < originalArray.length; i ++) {
			// boundCallback(originalArray[i], i, originalArray);
			callback(originalArray[i], i, originalArray);
		}
	};
	tests({
		'It should run callback function originalArray.length times.': function() {
			var numberOfTimesCallbackHasRun = 0;
			myForEach([1, 2, 3], function() {
				numberOfTimesCallbackHasRun ++;
			});
			eq(numberOfTimesCallbackHasRun, 3);
		},
		'It should return undefined.': function() {
			var newArray = myForEach([1, 2, 3], function(){});
			eq(newArray, undefined) 
		},
		'It should pass in the ith element in originalArray as first argument to callback.': function() {
			myForEach([1], function(number) {
				eq(1, number);
			});
		},
		'It should pass in the index of each postiion in originalArray as second argument to callback.': function() {
			myForEach([1], function(number, index) {
				eq(0, index);
			});
		},
		'It should pass in originalArray as third argument to callback.': function() {
			var testArray = [1, 2, 3];
			myForEach(testArray, function(number, index, originalArray) {
				eq(testArray, originalArray);
			});
		},
		'It should accept an optional this object.': function() {
			myForEach([1], function() {
				eq(this.description, 'I am an optional this object inside the callback.');
			}, {description: 'I am an optional this object inside the callback.'});
		},
		'It should not change originalArray.': function() {		
			var originalArray = [1];
			var testArray = [];
			myForEach(originalArray, function(num) {
				testArray.push(num + 1);
				eq(testArray[0], 2); 
			});
			eq(originalArray[0], 1);
		},
		'It should not access index properties that are deleted or unitialized (eg sparse arrays: undefined props).': function() {
			var originalArray = [1, 2, 3];
			myForEach(originalArray, function(num) {
				if (num === 1) {
					originalArray.shift();
				}
			}); 
			eq(originalArray[1], 3); // 2 should now be removed from the array; the second element === 3.
		},
	});
</script>