如何让回调与“this"一起工作?在类范围内 [英] How to get callback to work with "this" in class scope

问题描述

我有一个关于以下代码打印this.text"的问题.

I have a question about following code to print out "this.text".

我需要一个包装函数来让它工作.这太麻烦了.

I need to have a wrapper function to make it work. This is too troublesome.

有没有更简单的方法(没有额外的包装器)来让它工作?

Is there a simpler way (without additional wrapper) to get it work?

  function Class1() {
    this.text = "test";
  }

  Class1.prototype.show = function() {
    console.log(this);
    console.log(this.text);
  }

  var testClass = new Class1();

  function funWithCallBack(cb) {
    cb();
  }

  // it will show "undefined" because "this" scope changes to window
  funWithCallBack(testClass.show); 

  function wrapper() {
    testClass.show();
  }

  // this one will work but troublesome
  funWithCallBack(wrapper)

推荐答案

你可以像这样使用匿名函数:

You can use an anonymous function like this:

// it will show "undefined" because "this" scope changes to window
funWithCallBack(testClass.show); 

为此:

// anonymous function to use the right object for the method
funWithCallBack(function() {
    testClass.show()
}); 

<小时>

出现您的问题是因为当您将 testClass.show 作为回调传递时，它只获取函数引用，不再与 testClass 关联.但是，您可以创建一个临时函数，使用 .bind()，但在一些较旧的浏览器中不支持，这就是为什么我通常只使用匿名函数.

---

Your problem occurs because when you pass testClass.show as the callback, it just gets the function reference and there is no association with testClass any more. But, you can create a temporary function that binds them together using .bind(), but it isn't supported in some older browsers which is why I generally just use the anonymous function.

.bind() 实现如下所示:

// use .bind() to make sure the method is called in the right object context
funWithCallBack(testClass.show.bind(testClass)); 

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