Weighted random function. Should be used with lists smaller than 100. Passed that is not efficient.

weightedRandom.js

// array of items. Weight must add up to 100
// video1 = 20%, vieo2 = 50%, video3 = 10%, video4 = 20%
var items = ['Video1', 'Video2', 'Video3', 'Video4'];
var weights = [20, 50, 10, 20];

/**
 * Return a random value from aItems based on aWeights
 * @param  {array} aItems   Array of you items.
 * @param  {array} aWeights Array of weights that match items.
 * @return {String}         Selected item.
 */
var weightedRandom = function(aItems, aWeights){
    var sum = 0;
    var rand = Math.floor(Math.random() * (100 - 0) + 0);

    for (var i = aWeights.length - 1; i >= 0; i--) {sum += aWeights[i]};
    if( sum > 100 ) { throw new Exception("WeightsExceed100")};

    // Create array with
    var weightedList = [];
    for (var i = aItems.length - 1; i >= 0; i--) {
        for (var x = aWeights[i] - 1; x >= 0; x--) {
            weightedList.push(aItems[i]);
        };
    };
    return weightedList[rand];
};

// Call function example
weightedRandom(items, weights);