js抽奖概率算法

直接通过数组中prob值来控制概率，值越大概率越高，值越小，概率越低

<script>
	
function getRand(obj) {
    this.obj = obj;
    return this.init();
}

//获取几率总和
getRand.prototype.sum = function(key) {
    var self = this;
    var obj = this.obj;
    var sum = 0;
    for (var i in obj) {
        sum += obj[i][key];
    }
    return sum;
};

//取得结果
getRand.prototype.init = function() {
    var result = null;
    var self = this;
    var obj = this.obj;
    var sum = this.sum('prob'); //几率总和
    for (var i in obj) {
        var rand = parseInt(Math.random() * sum);
        if (rand <= obj[i].prob) {
            result = obj[i];
            break;
        } else {
            sum -= obj[i].prob;
        }
    }
    return result;
};


//几率数组
var obj = [{
        name: '结果一',
        prob: 1
    },
    {
        name: '结果二',
        prob: 5
    },
    {
        name: '结果三',
        prob: 39
    },
    {
        name: '结果四',
        prob: 60
    },
    {
        name: '结果五',
        prob: 703
    },
];

//使用方法
// $result = new getRand(obj);

//测试数据，循环1000次取得每个数据出现的次数
var record = [];
for (var i = 0; i <= 100; i++) {
    var result = new getRand(obj);
    var index = false;
    for (var j in record) {
        if (record[j].name == result['name']) {
            index = j;
			document.write("第"+i+"次，"+record[j].name+"<br>");
            break;
        }
    }
    if (index !== false) {
        record[index].num += 1;
    } else {
        record.push({
            name: result['name'],
            num: 1
        });
    }
	
}

</script>