javascript - javascript类中的自动增量值

Question

我试图在每次实例化该类的新实例时自动增加一个属性值。这是我的类构造函数的样子(我将其抽象了一点):

var Playlist = function(player, args){
    var that = this;
    this.id = ?; //Should auto increment
    this.tracks = [];
    this.ready = false;
    this.unloaded = args.length;
    this.callback = undefined;
    this.onready = function(c){
        that.callback = c;
    };
    this.add = function(tracks){
        for(var i = 0; i < tracks.length; i++){
            this.tracks.push(tracks[i]);
            this.resolve(i);
        }
    };
    this.resolve = function(i){
        SC.resolve(that.tracks[i]).then(function(data){
            that.tracks[i] = data;
            if(that.unloaded > 0){
                that.unloaded--;
                if(that.unloaded === 0){
                    that.ready = true;
                    that.callback();
                }
            }
        });
    };
    player.playlists.push(this);
    return this.add(args);
};

var playlist1 = new Playlist(player, [url1,url2...]); //Should be ID 0
var playlist2 = new Playlist(player, [url1,url2...]); //Should be ID 1

我不想定义在全局范围内递增的初始变量。谁能向我暗示正确的方向？干杯!

Answer 1

您可以使用 IIFE创建一个可以递增的私有(private)变量。

var Playlist = (function() {
  var nextID = 0;
  return function(player, args) {
    this.id = nextID++;
    ...
  };
})();