"这"关键字在事件方法中使用JavaScript原型对象时 [英] "this" keyword in event methods when using JavaScript prototype object

问题描述

我正在尝试在事件处理程序中使用JavaScript中的原型类的成员变量进行访问 - 我通常会使用this关键字（或that事件处理程序）。不用说，我遇到麻烦了。

I'm trying to access the member variables of a prototype class in JavaScript in an event handler -- something I'd typically use the "this" keyword for (or "that" [copy of this] in the case of event handlers). Needless to say, I'm running into some trouble.

例如，这个HTML片段：

Take, for example, this HTML snippet:

<a id="myLink" href="#">My Link</a>

此JavaScript代码：

And this JavaScript code:

function MyClass()
{
  this.field = "value"
  this.link = document.getElementById("myLink");
  this.link.onclick = this.EventMethod;
}

MyClass.prototype.NormalMethod = function()
{
  alert(this.field);
}

MyClass.prototype.EventMethod = function(e)
{
  alert(this.field);
}

实例化MyClass对象并调用NormalMethod与我预期的一样（警报说价值），但点击链接会导致一个未定义的值，因为this关键字现在引用事件目标（anchor（）HTML元素）。

Instantiating a MyClass object and calling NormalMethod works exactly like I expect it to (alert saying "value"), but clicking the link results in an undefined value because the "this" keyword now references the event target (the anchor () HTML element).

我是初学JavaScript样式的新手，但在过去，使用闭包，我只是在构造函数中复制了一个this：

I'm new to the prototype JavaScript style, but in the past, with closures, I've simply made a copy of "this" in the constructor:

var that = this;

然后，我可以通过该对象访问事件方法中的成员变量。这似乎不适用于原型代码。有没有另一种方法来实现这一点？

And then I could access members variables in event methods via the "that" object. That doesn't seem to work with prototype code. Is there another way to achieve this?

谢谢。

推荐答案

您的that = this闭合习语仍然适用：

Your "that=this" closure idiom is still applicable:

function MyClass()
{
    ...

    var that = this;
    this.link.onclick = function() {
        return that.EventMethod.apply(that, arguments);

        // that.EventMethod() works too here, however
        // the above ensures that the function closure
        // operates exactly as EventMethod itself does.

    };
}

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