jQuery问题：这究竟是什么意思？ [英] jQuery question: what does it really mean?

问题描述

(function($, window, undefined){
  ... jquery code... 
})(jQuery, window);

这究竟是什么意思？它是否也意味着 $（文件）.ready（）？或者只是两个不同的东西？

What does it really mean? Does it also mean $(document).ready()? Or just two different things?

推荐答案

已经有两个答案，但这是我对代码缺失结束的猜测：

There are already two answers but this is my guess on the missing end of the code:

(function ($, window, undefined) {
  // ... jquery code... 
})(jQuery, window);

注意：三个参数是预期但两个是提供的。

Note: three parameters are expected but two are supplied.

它基本上是做什么的：

1. 给出一个私人的花括号里面的范围，所以在里面声明的任何 var 在
之外是不可见的。

2. 使私有 $ jQuery 的快捷方式，而不依赖于全局设置的此快捷方式（例如。 jQuery.noconflict（）可能已被调用，这仍然可以工作）


3. 创建一个词法窗口变量，这意味着更快地查找全局变量


4. 确保 undefined 在大括号之间的范围内确实是未定义的，即使有人写了类似 undefined =now now the defined; 在全局范围内，因为 undefined 实际上可以重新定义（这是该语言的错误）。

1. gives a private scope inside curly braces, so any var declared inside is not visible outside
2. makes a private $ shortcut to jQuery without relying on this shortcut being set globally (eg. jQuery.noconflict() might have been called and this would still work)
3. makes a lexical window variable that would mean faster lookups for global variables
4. makes sure that undefined is indeed undefined in the scope between curly braces, even if someone has written something like undefined = "now it's defined"; in the global scope, because undefined can actually be redefined (this is a mistake of the language).

此模式立即称为调用函数，或简短的立即函数，或自调用匿名函数或其他一些名称。基本思路是：

This pattern is known as immediately invoked function, or immediate function for short, or self-invoking anonymous function, or some other names. The basic idea is that:

(function (x, y) {
    // ...
})(1, 2);

或：

(function (x, y) {
    // ...
}(1, 2));

表示相同：

function myFunction (x, y) {
    // ...
}
myFunction(1, 2);

但不需要为您的函数指定任何名称并污染命名空间。

but without the need to give any name to your function and pollute the namespace.

回到你的问题，这并不意味着 $（文件）.ready（）或类似的东西，但这意味着您可以使用 $（document）.ready（） inside 而不是 jQuery（document）.ready（）即使 $ 快捷方式在外面不可用。

Going back to your question, this doesn't mean $(document).ready() or anything like that, but it means that you can use $(document).ready() inside instead of jQuery(document).ready() even if the $ shortcut is not available outside.

这个例子实际上可以解释它更好，即使它没有在任何地方使用：

This example may actually explain it better, even if it isn't used anywhere:

(function (JQ, window, undefined) {

    JQ(document).ready(function () {
        // this is run when document is ready
    });

})(jQuery, window);

现在可以调用jQuery而不是 $ as JQ 并使用 JQ（文件）.ready（）而不是 $（文件） .ready（） - 它可能看起来不太有用，但它显示了当你有这样的代码时会发生什么。

Now instead of $ you can call jQuery as JQ and use JQ(document).ready() instead of $(document).ready() – it may not seem very useful but it shows what happens when you have a code like that.

作为旁注我可以补充说，多亏了这个模式，你实际上并不需要语言中的变量声明，只需要函数参数。而不是：

As a side note I might add that thanks to this pattern you don't actually need variable declarations in the language but only function arguments. Instead of:

var x = 10;
alert(x * x * x);

你可以使用：

(function (x) {
    alert(x * x * x);
})(10);

确实是这样的函数：

function square (x) {
    // some code ...
    var result = x * x;
    return result;
}

完全等同于：

function square (x, result) {
    // some code ...
    result = x * x;
    return result;
}

因为JavaScript中的提升机制会使结果变量可用（但未定义）甚至在两种情况下的声明和赋值之前（在 //某些代码... 部分）。这通常是一个混乱的来源，但实际上非常有趣且非常强大。

because of the hoisting mechanism in JavaScript that would make the result variable available (but undefined) even before the declaration and assignment in both cases (in the // some code ... part). This is often a source of confusion but is actually quite interesting and extremely powerful.

另请参阅我最近更新的其他回答问题：
帮助理解JavaScript全局减排技术，了解有关此主题的更多信息。

See also my other recently updated answer to the question: Help understanding JavaScript global abatement techniques for more info on this subject.

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