I already know that apply and call are similar functions which set this (context of a function).(我已经知道apply和call是用于设置this相似函数（函数的上下文）。)
bind() method ?(但是我什么时候应该使用bind()方法呢？)
var obj = {
x: 81,
getX: function() {
return this.x;
}
};
alert(obj.getX.bind(obj)());
alert(obj.getX.call(obj));
alert(obj.getX.apply(obj));
jsbin(jsbin)
ask by Royi Namir translate from so
Use .bind() when you want that function to later be called with a certain context, useful in events.(当您希望以后在特定上下文中调用该函数时，请使用.bind() ，在事件中很有用。)
.call() or .apply() when you want to invoke the function immediately, and modify the context.(若要立即调用该函数并修改上下文，请使用.apply() .call()或.apply() 。)
Call/apply call the function immediately, whereas bind returns a function that, when later executed, will have the correct context set for calling the original function.(调用/应用立即调用该函数，而bind返回一个函数，该函数稍后执行时，将具有正确的上下文集来调用原始函数。) This way you can maintain context in async callbacks and events.(这样，您可以在异步回调和事件中维护上下文。)
I do this a lot:(我经常这样做：)
function MyObject(element) {
this.elm = element;
element.addEventListener('click', this.onClick.bind(this), false);
};
MyObject.prototype.onClick = function(e) {
var t=this; //do something with [t]...
//without bind the context of this function wouldn't be a MyObject
//instance as you would normally expect.
};
I use it extensively in Node.js for async callbacks that I want to pass a member method for, but still want the context to be the instance that started the async action.(我在Node.js中将它广泛用于异步回调，我想为其传递成员方法，但仍希望上下文成为启动异步操作的实例。)
A simple, naive implementation of bind would be like:(一个简单，简单的bind实现是：)
Function.prototype.bind = function(ctx) {
var fn = this;
return function() {
fn.apply(ctx, arguments);
};
};
There is more to it (like passing other args), but you can read more about it and see the real implementation on the MDN .(它还有更多的功能（就像传递其他args一样），但是您可以阅读更多有关它的内容，并查看MDN上的实际实现。)
Hope this helps.(希望这可以帮助。) 