Javascript“对象没有方法”错误

Question

This seems to be a popular question on this site but previous answers haven't solved this instance of the problem.

I have the beginnings of a game engine on a node.js server but when I set it going I get the following error occuring in the loop method: Object #<Timer> has no method update .

I thought I was setting the prototype to have an update method with GameEngine.prototype.update = function(){ ... };

Any help in solving this problem would be much appreciated. Thank you.

Here's the entire code:

function GameEngine(){
    this.fps = 1000/60;
    this.deltaTime = 0;
    this.lastUpdateTime = 0;
    this.entities = [];
}

GameEngine.prototype.update = function(){
    for(var x in this.entities){
        this.entities[x].update();
    }
}

GameEngine.prototype.loop = function(){
    var now = Date.now();
    this.deltaTime = now - this.lastUpdateTime;
    this.update();
    this.lastUpdateTime = now;
}

GameEngine.prototype.start = function(){
    setInterval(this.loop, this.fps);
}

GameEngine.prototype.addEntity = function(entity){
    this.entities.push(entity);
}

var game = new GameEngine();
game.start();

Answer 1

This seems to be a popular question on this site

Yes.

but previous answers haven't solved this instance of the problem.

really? Which ones have you found?

---

The context of the "method" ( this ) is lost when the function is executed by a timeout/event listener/etc.

GameEngine.prototype.start = function(){
    var that = this;
    setInterval(function(){
       that.loop();
    }, this.fps);
}

or

GameEngine.prototype.start = function(){
    setInterval(this.loop.bind(this), this.fps);
}