寫了一個抽獎的jquery外掛和計算概率的方法， 結合起來就是一個簡單的概率抽獎， 不過實際專案中基本不會把抽獎概率的計算放在前端處理~。

demo

lottery.jquery.js

$.fn.extend({
    lottery: function(conf) { 
        var def = {
            lotIndex: 0,            // 抽中的索引
            item: "li",
            onClass: "on",
            speedStart: 50,         // 初始速度
            speedEnd: 400,          // 結束速度
            speedType: "",          // 預設勻速 可選 change: 減速
            overTime: 5000,         // 抽獎時長（最短）
            overCallback: function() {}     // 抽獎結束後的回撥函式
        };
        
        if (typeof conf.lotIndex === "undefined") {
            return
        }
        
        def = $.extend({}, def, conf);
        
        var $lotteryList = $(this),
            lotteryControl = {};
        
        lotteryControl = {
            $el: $lotteryList,
            item: def.item,
            itemLen: 0,
            index: 0,
            speedType: def.speedType,
            speedStart: def.speedStart,
            speed: def.speedStart,
            speedEnd: def.speedEnd,
            a: 0,                             // 加速度
            nowTime: 0,                     // 抽獎已進行時間
            overFlag: false,                // 抽獎是否結束
            onClass: def.onClass,
            lotIndex: def.lotIndex,
            overTime: def.overTime,
            overCallback: def.overCallback,
            init: function() {
                this.$items = this.$el.find(this.item);
                this.itemLen = this.$items.length;
                this.a = (this.speedEnd - this.speed) / this.overTime;

                if (this.lotIndex >= this.itemLen) {
                    this.error();
                } else {

                    this.start();
                }
            },
            start: function() {
                var self = this;

                this.play();
                this.setStop();

                switch (this.speedType) {
                    case "change":
                        this.changeSpeed();
                        break;
                }
            },
            play: function() {
                var $items = this.$items;

                $items.eq(this.index - 1).removeClass(this.onClass);
                $items.eq(this.index).addClass(this.onClass);

                if (this.overFlag && this.index === this.lotIndex) {
                    this.stop();
                } else {
                    this.next();
                }
            },
            next: function() {
                var self = this;

                this.index++;
                this.index = this.index === this.itemLen ? 0 : this.index;

                setTimeout(function() {
                    self.play();
                }, this.speed);

            },

            changeSpeed: function() {
                var self = this;

                setTimeout(function() {
                    self.nowTime += self.speed;

                    if (!self.overFlag) {
                        self.speed = self.speedStart + self.a * self.nowTime;

                        self.changeSpeed();
                    }
                }, this.speed);

            },
            setStop: function() {
                var self = this;

                setTimeout(function() {
                    self.overFlag = true;
                }, this.overTime);
            },
            stop: function() {
                this.overCallback();
            },
            error: function() {
                console.log("error.......");
            }
        };
        
        lotteryControl.init( );
        
        return this;
    }
});
            
 

概率計算

function Probability(conf) {
    this.probArr = conf || [];
    this.range = [],
    this.len = this.probArr.length;
    if (this.len > 0) { 
        this.init();
    }
}
Probability.prototype = {
    init: function() {
        this.setRange();
    },
    get: function() { 
        var len = this.len,
            range = this.range,
            last,
            randNum, 
            i = 0; 
        if (len === 0) {
            return;
        } else if(len === 1) {
            return 0;
        } 
        last = range[len -1];
        randNum = Math.floor(last* Math.random()); 
        for (; i < len; i++) { 
            if (randNum < range[i]) {
                break;
            }
        } 
        return i;
    }, 
    setRange: function() {
        var range = [],
            probArr = this.probArr,
            i = 0,
            len = probArr.length; 
        for(; i<len; i++) {
            var now = probArr[i],
                last = range[i-1] || 0; 
            range.push(now+last);
        }  
        this.range = range;
    }
};