javascript ！javascript中的前一个函数？
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! preceding function in javascript?
提问by rg88
Possible Duplicate:
What does the exclamation mark do before the function?
可能的重复：
感叹号在函数之前有什么作用？
I saw a function formatted like this today for the first time:
今天第一次看到这样格式化的函数：
!function(){}();
What is the preceding exclamation mark for? I assume it functions the same as:
前面的感叹号是什么意思？我假设它的功能与：
(function(){})();
But... what's going on here?
但是……这是怎么回事？
回答by Mike Lewis
The preceding !takes the un-parseable statement, and allows it to to be parsed by the JS engine, which in turn returns true.
前面!的语句采用 un-parseable 语句，并允许它被 JS 引擎解析，然后返回 true。
function(){}();
SyntaxError: Unexpected token (
!function(){}();
>>true
回答by ThiefMaster
It simply makes the JavaScript parser parse it as an expression, which is necessary to execute it.
它只是让 JavaScript 解析器将其解析为一个表达式，这是执行它所必需的。
回答by Ming-Tang
I've tried it, it returned true.
The function returns undefined, and !undefinedis true.
我试过了，它返回true。函数返回undefined，并且!undefined为真。
!function(){}();
^ ^ ^
C A B
- A.
function(){}is an empty anonymous function - B.
()executes the function (A), returningundefined - C.
!negatesundefined, which becomestrue
- A.
function(){}是一个空的匿名函数 - B.
()执行函数（A），返回undefined - C.
!否定undefined, 变成true
I think they used that trick for a code golf or an obfuscated code. It is a bad practice to practially use that
我认为他们将这个技巧用于代码高尔夫或混淆代码。实际使用它是一种不好的做法
Try javascript:alert(!function(){}())in your browser address bar
javascript:alert(!function(){}())在浏览器地址栏中尝试
