How to call requestAnimFrame on an object method?

问题:

Say I have the following object:

function Foo(value){
    this.bar = value;
    this.update();
}
Foo.prototype.update = function(){
    console.log(this.bar);
    this.bar++;
    requestAnimationFrame(this.update);
}
Foo.prototype.setBar(value){
    this.bar = value;
}

This does not work. FireFox gives me an error:

NS_ERROR_ILLEGAL_VALUE: Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE) [nsIDOMWindow.requestAnimationFrame]

I would like to know why, and what other solution could be used instead to call an object's update method without calling it from your main function(i.e. while keeping the object anonymous).

回答1:

requestAnimationFrame doesn’t bind this to anything, like any direct call. You can do that manually using Function.prototype.bind:

Foo.prototype.update = function(){
    console.log(this.bar);
    this.bar++;
    requestAnimationFrame(Foo.prototype.update.bind(this));
};

Binding permanently is another way:

function Foo() {
    …
    this.update = this.update.bind(this);
    this.update();
}