Javascript 自调用函数之前的分号？
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Semicolon before self-invoking function?
提问by 7elephant
What is the benefit of using semicolon before a self-invoking function in JavaScript. I saw this approach in few popular jQuery plugins and I'm curious to find if this is the next awesome thing in JavaScript that I dont know. Thanks in advance, guys!
在 JavaScript 中的自调用函数之前使用分号有什么好处。我在几个流行的 jQuery 插件中看到了这种方法，我很好奇这是否是 JavaScript 中我不知道的下一个很棒的东西。提前致谢，伙计们！
回答by amoebe
If you concatenate two files with self-invoking functions together that look like this:
如果将两个具有自调用函数的文件连接在一起，如下所示：
File A:
文件A：
(function(){...A...})()
File B:
文件乙：
(function(){...B...})()
File A+B:
文件 A+B：
(function(){...A...})()(function(){...B...})()
You have two statements without separator. This happens when you cat files together and then minify them.
你有两个没有分隔符的语句。当您将文件放在一起然后缩小它们时会发生这种情况。
Now the author of file B puts a semicolon in front:
现在文件 B 的作者在前面放了一个分号：
File B2:
文件 B2：
;(function(){...B2...})()
And you'll get a working script:
你会得到一个工作脚本：
(function(){...A...})();(function(){...B2...})()
回答by Mike Samuel
Self-invoking functions are surrounded by parentheses, and in JavaScript parentheses are overloaded to mean
自调用函数被括号包围，在 JavaScript 中括号被重载的意思是
- Grouping expressions to override precedence:
(x + y) * z - Function application :
f()
- 分组表达式以覆盖优先级：
(x + y) * z - 功能应用：
f()
Putting a semicolon before the function prevents the function from becoming an argument to whatever precedes it when the parentheses become confused with function application.
当括号与函数应用程序混淆时，在函数前放置分号可防止函数成为它前面任何内容的参数。
Consider
考虑
var x = 42
(function () { ... })()
is the same as
是相同的
var x = 42(function () { ... })()
but
但
var x = 42
;
(function () { ... })()
is the same as
是相同的
var x = 42;
(function () { ... })()
回答by Mike Samuel
Iwrite allJavaScript in a semicolon-free style. When writing without semicolons at the end of every line, due to Automatic Semicolon Insertion (ASI), there are a few special cases that can "be confusing" at first:
我以无分号的风格编写所有JavaScript。当每行末尾没有分号时，由于自动分号插入 (ASI)，有一些特殊情况最初可能会“令人困惑”：
Starting a top-level expression with an operator, a
((open parenthesis) in this case, which like most other operators, can continuethe previous expression and thus suppresses the "automatic insertion of a semicolon". (This generally only occurswhen using a self invoking function.)Just kidding about #2: there isn't one! (Learn only one rule and you too can enjoy life without extra semicolons ;-)
使用 operator 开始顶级表达式，
(在这种情况下是一个（左括号），与大多数其他 operator 一样，可以继续前一个表达式，从而抑制“自动插入分号”。（这通常仅在使用自调用函数时发生。）开个玩笑#2：没有！（只学习一个规则，你也可以享受没有额外分号的生活;-)
Since I write in a semicolon-free style I thus alwayswrite it as (where the function-expression can naturally span multiple lines):
由于我以无分号的风格编写，因此我总是将其写为（函数表达式可以自然地跨越多行）：
;(FunctionExpression)()
In mycase it isn't about "safety" or trying to "catch an error" (honestly, if your style is to use semi-colons and you forget a semi-colon, then you've already created the error elsewhereand writing a ;at the start for "safety" is hogwash). No; in my case it is done for consistencywith knowledgeof my chosen style and "knowing" that starting a line with an operatorcan continue an expression from a previous line.
在我的情况下，这与“安全”或试图“捕捉错误”无关（老实说，如果您的风格是使用分号而您忘记了分号，那么您已经在其他地方创建了错误并写作;“安全”开头的a是胡说八道）。不; 在我的情况下，这样做是为了与我选择的样式的知识保持一致，并且“知道”使用运算符开始一行可以从前一行继续表达式。
See JavaScript: Semicolon Insertion (Everything You Need To Know)for the details (it is by far the best article I have seen on the subject).
有关详细信息，请参阅JavaScript: Semicolon Insertion (Everything You Need To Know)（这是迄今为止我在该主题上看到的最好的文章）。
Happy coding.
快乐编码。
回答by Francis
For me, the semi colon was triggering an error in Internet Explorer 8 (or at least that's what IETester said), and preventing the ui tabs from working properly.
对我来说，分号在 Internet Explorer 8 中触发了错误（或者至少 IETester 是这么说的），并阻止了 ui 选项卡正常工作。
The error message was Invalid character in jquery.all.ui.js Line: 1. Char: 1.
错误消息是Invalid character in jquery.all.ui.js Line: 1. Char: 1。
I stumbled on the semi-colon completely by chance.
When I removed the ;from the ;(function($)it worked, seemingly without side-effects or loss of functionality.
I am using Drupal, don't know whether this has anything to do with the matter.
我完全偶然发现了分号。当我;从;(function($)它的工作中删除它时，似乎没有副作用或功能损失。我正在使用Drupal，不知道这是否与此事有关。
