网页缓存音频文件循环播放，背景音乐循环播放

bgm.start();

var bgm = {
    typedef : ['ji','niu','yang','niao'],
    buffer  : {},
    context : null,
    timeout : 3000,
    start: function(){
        this.cacheBuf();
        this.run();
    },
    run: function(){
        setTimeout(function(){
            if(this.context != null){
                this.context.close();
                this.context = null;
            }
            var _li = Math.floor((Math.random()*this.typedef.length));
            this.audioPlay(this.typedef[_li]);
            this.run();
        }, this.timeout);
    },
    audioPlay: function(tp){
        var _this = this;
        var _buff = this.buffer[tp].slice(0, this.buffer[tp].byteLength);
        this.context = new (window.AudioContext || window.webkitAudioContext)();
        this.context.decodeAudioData(_buff, function(buffer){
            var source = _this.context.createBufferSource();
            source.buffer = buffer;
            source.connect(_this.context.destination);
            source.start(0);
        });
    },
    cacheBuf: function(){for(i in this.typedef){
            _tp = this.typedef[i];
            this.getbuf('static/audio/'+ _tp +'.mp3', _tp);
        }
    },
    getbuf: function(url, tp){
        var _this = this;
        var xhr = new XMLHttpRequest();
        xhr.open('GET', url, true);
        xhr.responseType = 'arraybuffer';
        xhr.onreadystatechange = function () {
            if (xhr.readyState === 4 && xhr.status === 200) {
                _this.buffer[tp] = xhr.response;
            }
        };
        xhr.send();
    }
};