我可以将本地var设置为'this'以在匿名回调函数中引用它吗？

Question

I would like to reference 'this' in a callback function, but there is no guarantee that 'this' will refer to the correct object. Is it appropriate to create a local variable referencing 'this' and use that variable inside the anonymous function?

Example:

var MyClass = function (property) {
  this.property = property;
  someAsynchronousFunction(property, function (result) {
    this.otherProperty = result; // 'this' could be wrong
  });
};

The problem is, the asynchronous function may call the provided callback from an arbitrary context (which is often outside of my control, eg when using libraries).

My proposed solution is:

var MyClass = function (property) {
  this.property = property;
  var myClass = this;
  someAsynchronousFunction(property, function (result) {
    myClass.otherProperty = result; // references the right 'this'
  });
};

But I was looking to see if there are other strategies, or if this solution is problematic in any way.

Answer 1

What you've done is the classical way of making sure you refer to the correct object, though you should define it locally , ie:

function(property) {
    var that = this;

    someFunc(function(result) {
        that.property = whatever;
    }
}

Alternatively, in modern browsers you can bind it explicitly:

someFunc(function(result) {
    this.property = whatever;
}.bind(this));

See also: bind()

Libraries such as jQuery support the latter functionality as a proxy function that more browsers support and can be simplified into this reusable function:

function proxy(fn, ctx)
{
    return function() {
        return fn.apply(ctx, arguments);
    }
}

And to use it:

someFunc(proxy(function(result) {
    this.property = whatever;
}, this));

Answer 2

是的，那很好，但是不要像您一样使用隐式全局变量，而要使用局部变量：

var myClass = this;