JavaScript中的闭包/回调函数的用例是什么？ [英] What are the use cases for closures/callback functions in JavaScript?

问题描述

我正在听Crockford关于JavaScript闭包的讨论，并相信信息隐藏的好处，但我并不完全了解何时使用回调函数。

I was listening to Crockford's talk on JavaScript closures and am convinced of the benefit of information hiding, but I do not have a firm understanding of when to use callback functions.

这是一个真正的声明，一个人可以完成相同的功能，有或没有回调。

It is mostly a true statement that a person could accomplish the same functionality with or without callbacks.

作为编写代码的人，我应该保持什么启发式或提示在确定何时使用回调/关闭？

As someone who is writing code, what heuristics or cues should I keep in mind when determining when to use callbacks/closures?

我不是在寻找覆盖语句Closures make更安全的代码，而是一个实用示例或规则列表

I am not looking for the blanket statement 'Closures make more secure code', rather a list of practical examples or rules of thumb for when callbacks are the right idea.

Crockford的演讲：
http://www.yuiblog.com/blog/2010/04/08/video-crockonjs-5/

Crockford's Presentation: http://www.yuiblog.com/blog/2010/04/08/video-crockonjs-5/

推荐答案

首先：

• 回调：作为参数传递给另一个函数，通常被称为事件发生的结果。


• 关闭：保留的范围。也就是说当您在另一个函数中声明一个函数时，外部函数的范围在内函数内是可访问的。

• Callback: A function passed as an argument to another function, usually to be called as a result of an event occurring.
• Closure: A retained scope. I.e. the concept that when you declare a function within another function, the outer function's scope is accessible within the inner function.

回调也可以是闭包，但不总是。

Callbacks can also be closures, but are not always.

这是一个回调：

someProcess(myCallback);

function myCallback() {
    alert('Done...');
}

function someProcess(callback) {
    // does stuff...
    // ...
    callback();
}

结束：

function foo(msg) {

    function bar() {
        // I can access foo's scope
        // (i.e. bar can access everything that foo can access)
        alert(msg);
    }

    return bar;

}

foo('hello')(); // alerts "hello"

闭包的一个常见用法是提供信息隐藏在给语言带来某种封装。请查看模块模式以查看此操作。

One common usage of closures is to provide information-hiding, which is helpful in bringing some kind of encapsulation to the language. Have a look at the module pattern to see this in action.

另一种常见的用法是将事件处理程序绑定到元素。例如

Another common usage is when binding event handlers to elements. E.g.

var myElements = [ /* DOM Collection */ ];

for (var i = 0; i < 100; ++i) {
    myElements[i].onclick = function() {
        alert( 'You clicked on: ' + i );
    };
}

这不行。到该元素被点击时，变量 i 为 99 。为了使其正常工作，我们使用一个闭包来捕获 i 的值：

That wouldn't work. By the time the element is clicked, the variable i is 99. To make this work properly we cold use a closure to capture the value of i:

function getHandler(n) {
    return function() {
        alert( 'You clicked on: ' + n );
    };
}

for (var i = 0; i < 100; ++i) {
    myElements[i].onclick = getHandler(i);
}

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