这个javascript语法是什么意思？ [英] What does this javascript syntax mean?

问题描述

我正在尝试理解由Asp.Net Ajax Toolkit生成的脚本，该脚本目前正在提供预期的对象（如果我将PopupControlExtender放在更新面板中，则错误消失）。

I am trying to understand a script generated by Asp.Net Ajax Toolkit, which is currently giving an "object expected" (error goes away if I place my PopupControlExtender in an update panel).

document.getElementById('ctl00_ValidationSummary1').dispose = function() {
    Array.remove(Page_ValidationSummaries, document.getElementById('ctl00_ValidationSummary1'));
}
(function() {var fn = function() {AjaxControlToolkit.ModalPopupBehavior.invokeViaServer('ctl00_c1_componentCategoryListUC_componentCategoryGrid_modalPopupExtender', true); Sys.Application.remove_load(fn);};Sys.Application.add_load(fn);})();

我在这里看到的是：

someobject.someevent = function() {
    dosth;
} /* Get ready, I am about to do sth crazy ... */
(function() { dosth; })(); /* you did what? */

这种语法是什么意思？

编辑：我特别好奇（function（）{...}）（）在另一个函数的结束后立即出现}。

I am specifically curious about (function () { ... })() coming immediately after another function's ending }.

编辑：原来，ajax家伙忘记在事件处理程序分配后放置分号。

Turns out, ajax guys forgot to place a semicolon after the event handler assignment.

推荐答案

(function() { dosth; })();

语法声明一个匿名函数，然后立即执行它。这相当于这样做：

syntax declares an anonymous function, and then executes it immediately. It's equivalent to doing this:

 var myFun = (function() { dosth; });
 myFun();

但没有临时变量。

从广义上讲，这类似于执行任何 dosth ;但是创建一个函数对象会引入一个新的变量范围（由于闭包），因此这通常用于解决范围问题。

Broadly speaking this is similar to just executing whatever dosth is; but creating a function object introduces a new scope for variables (due to the closure), and thus this is often used to work around issues with scoping.

在特定情况下你引用过，我认为没有任何理由说这一点特别必要。然而，它可以这样做有两个原因 - 最终的Javascript本身是由一些自动过程生成的，无法判断是否需要闭包;或者它是由一个决定永远把功能包装起来的人来写的。

In the specific case you've quoted, I don't see any reason why this would be particularly necessary. However it could be done like this for two reasons - either the final Javascript itself is generated by some automatic process that can't tell whether the closure is needed; or it was written by a human who decided to always wrap things in functions to be safe.

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