myFilter.html

<script src="..\my-jsArrayMethods\simpletest.js"></script>
<script>

// The filter() method creates a new array with all elements that pass the test implemented by the provided function.

// Parameters:
    // Callback: Function is a predicate, to test each element of the array. Return true to keep the element, false otherwise
    // Takes three arguments:
        // Element: The current element being processed in the array.
        // Index (Optional): The index of the current element being processed in the array.
        // Array (Optional): The array filter was called upon.
    // This Arg (Optional): Value to use as this when executing callback.
// Return value: A new array with the elements that pass the test. If no elements pass the test, an empty array will be returned.

function myFilter(originalArray, callback, optionalThis) {
    for (i = 0; i < originalArray.length; i ++) {
        if (optionalThis) {
            callback = callback.bind(optionalThis);
        }
        var filteredArray = [];
        for (var i = 0; i < originalArray.length; i ++) {
            // if (boundCallback(originalArray[i], i, originalArray)) {
                if (callback(originalArray[i], i, originalArray)) {
                filteredArray.push(originalArray[i]);
            }
        }
        return filteredArray;
    }
};

tests({
 	'It should run a callback function originalArray.length times.': function() {
         var callbackCounter = 0;
         myFilter([1, 2, 3], function() {
            callbackCounter ++;
         });
         eq(callbackCounter, 3);
     },
    'It should pass in the ith el as the first argument to callback.': function() {
        myFilter([1], function (el) {
            eq(el, 1);
        });
    },
    'It should pass in the index of current el being processed as optional second arg in callback. ': function() {
        myFilter([1], function(el, index) {
            eq(0, index);
        });
    },
    'It should pass in the originalArray as optional third arg in callback.': function() {
        var testArray = [1, 2, 3];
        myFilter(testArray, function(el, index, originalArray) {
            eq(testArray, originalArray)
        });
    },
    'It should accept an optional this object.': function() {
        myFilter([1], function() {
            eq(this.name, 'filterTest');
        }, {name: 'filterTest'});
    },
    'It should return an array.': function() {
        var testArray = [1, 2, 3];
        var filteredArray = myFilter(testArray, function() {});
        eq(Array.isArray(filteredArray), true);
    },
    'It should return a new array, not the array being filtered.': function() {
        var testArray = [1, 2, 3];
        var filteredArray = myFilter(testArray, function() {});
        eq(testArray === filteredArray, false);
    },
    'It should return a new array that only has elements where callback() is true.': function() {
        var filteredArray = myFilter([1, 2], function(el) {
            return el > 1;
        });
        eq(filteredArray.length, 1);
        eq(filteredArray[0], 2);
    },
});
</script>