在requestAnimationFrame中设置正确的this-value [英] Setting correct this-value in requestAnimationFrame

问题描述

我有一个app-object构造函数，如下所示：

I have an app-object constructer that looks like this:

var app = function(loadedsettings) {

    return {
        init: function() {          
            this.loop();
        },

        loop: function() {
            this.update();
            window.requestAnimationFrame(this.loop);
        },

        update: function() {
            //loop through settings and call update on every object.
        },

        settings: [
             //array of settings objects, all with update methods. 
        ]
    };
}

然后当我这样做时：

var theApp = app(settings);
theApp.init();

我得到：

Uncaught TypeError: Object [object global] has no method 'update'

因为当调用requestAnimationFrame时，循环函数中的this-value设置为window。

because when requestAnimationFrame is called, the this-value inside the loop function is set to window.

是否有人知道如何调用requestAnimatinFrame并将'theApp'对象设置为this -值？

Does anybody know how to call requestAnimatinFrame with the 'theApp' object set as the this-value?

推荐答案

您可以创建一个绑定函数（具有固定的此） ，并将其传递给requestAnimationFrame：

You can create a bound function (with a fixed this), and pass that to requestAnimationFrame:

var app = function(loadedsettings) {

    return {
        init: function() {          
            this.loop();
        },

        loop: function() {
            this.update();
            window.requestAnimationFrame(this.loop.bind(this));
        },

        update: function() {
            //loop through settings and call update on every object.
        },

        settings: [
             //array of settings objects, all with update methods. 
        ]
    };
}

我认为支持requestAnimationFrame的浏览器将会也支持Function.prototype.bind，但是遇到没有的那个，可以使用polyfill。

I think that a browser which supports requestAnimationFrame will also support Function.prototype.bind, but in case you come across one that doesn't, there are polyfills available.

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