如何获得回调以使用“this”在类范围 [英] How to get callback to work with "this" in class scope

问题描述

我有一个关于下面的代码打印出this.text的问题。我需要有一个包装函数，使其工作。这太麻烦了。有没有一个更简单的方法（没有额外的包装）得到它的工作？

I have a question about following code to print out "this.text". I need to have a wrapper function to make it work. This is too troublesome. Is there a simpler way (without additional wrapper) to get it work?

感谢

  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

您可以使用如下匿名函数：

You can use an anonymous function like this:

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

：

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

---

出现您的问题，因为当您通过 testClass.show 作为回调，它只是获取函数引用，并且与 testClass 没有任何关联。但是，您可以创建一个临时函数，使用将它们绑定在一起 .bind（） ，但是在一些旧版本浏览器中不支持，因此我一般只使用匿名函数。

---

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（）实现将如下所示：

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

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