Question

Game.prototype.run = function() {
    window.setInterval(function() {
        var thisLoop = new Date().getTime();

        this.update();
        this.render();

        lastLoop = thisLoop;
    }, 1000 / this.fps);
};

game.js:198Uncaught TypeError: Object [object DOMWindow] has no method ‘update’

Why is this happening ?
“this” should relate to the Game object.

Answer 1

Cache the this variable, or use Function.bind:

Game.prototype.run = function() {
    var _this = this;
    window.setInterval(function() {
        var thisLoop = new Date().getTime();
        _this.update();
        _this.render();
        lastLoop = thisLoop;
    }, 1000 / this.fps);
};

Or, using Function.bind:

Game.prototype.run = function() {
    window.setInterval((function() {
        ... 
    }.bind(this), 1000 / this.fps);
};

this in a function passed to setInterval refers to the global window object, or is undefined (in strict mode).

Another method, similar to the first one. Pass this as a parameter to the function (so that no extra local variable is used):

Game.prototype.run = function() {
    window.setInterval(function(_this) {
        var thisLoop = new Date().getTime();
        _this.update();
        _this.render();
        lastLoop = thisLoop;
    }, 1000 / this.fps, this);
};