Edit in JSFiddle

function generateRandomArray(size, maxElement) {
    var array = [];
    for (var i = 0; i < size; i += 1) {
        array.push(Math.floor(Math.random() * (maxElement + 1)));
    }
    return array;
}

var new_big_array = generateRandomArray(1000000, 100); // generate array with 1 million elements

function sortArray(input_arr) {
    var startTimeStamp = new Date().getTime(),
        duration;

    input_arr.sort(function (a, b) { // sort array
        return a - b;
    });

    duration = new Date().getTime() - startTimeStamp; // javascript benchmark - difference between start and end time in milliseconds
    //alert('Sorting of array with 1 million elements lasts ' + duration + ' milliseconds;');
    document.getElementById('log').innerHTML = 'Sorting of array with 1 million elements lasts ' + duration + ' milliseconds;';
}

sortArray(new_big_array);

<div id="log"></div>