goodluck.js

/*obj 概率对象数组;
luck 概率数组，即obj数组元素意义对应;
对于给定的概率对象，该函数运行相当于：

var a = ['一等奖：宝马X6', '二等奖：苹果三件套', '三等奖：威戈背包', '继续努力！'];
var b = [1, 10, 100, 500];
goodluck(a, b) {
    var random = (1 + 10 + 100 + 500) * Math.random();
    random <= 500 || return a[3];
    random <= 600 || return a[2];
    random <= 610 || return a[1];
    random <= 611 || return a[0];
    return null;
};
*/

function goodluck(obj, luck) {
    var sum = 0,
        factor = 0,
        random = Math.random();

    for(var i = luck.length - 1; i >= 0; i--) {
        sum += luck[i]; // 统计概率总和
    };
    random *= sum; // 生成概率随机数
    for(var i = luck.length - 1; i >= 0; i--) {
        factor += luck[i];
        if(random <= factor) return obj[i];
    };
    return null;
};

/* test
var a = ['一等奖：宝马X6', '二等奖：苹果三件套', '三等奖：威戈背包', '继续努力！'];
var b = [100, 100, 100, 100];
console.log(goodluck(a, b));
*/