javascript - javascript iffy结构之间的区别

Question

这个问题已经有答案了:

var functionName = function() {} vs function functionName() {} (41 个回答)

已关闭 7 年前。

这些js函数结构有什么区别

(function () { console.log("Foo!"); }());

(function () { console.log("Foo!"); })();

;(function () { console.log("Foo!"); }());

+function() { console.log("done!"); }();

Answer 1

据我所知，前三个没有区别。

当您编写立即调用函数表达式时，外部参数括号可以存在于包装括号的内部和外部。将其视为具有相同目的的另一种语法。

所以这个:

(
    function() {
    }
());

还有这个:

(
    function() {
    }
)();

完全平等。

对于第三个示例，分号，在文件串联的情况下用作保护措施。当您编写代码时，您或 vendor 可能有一个不以分号结尾的脚本。在这种情况下，当您连接不以问号结尾的先前文件代码时，脚本将会中断。

示例

script-1.js

var name = 'Nikos';
console.log( name )

script-2.js

(
    function() {
       // Do some stuff here
    }
)();

concatenation.js

var name = 'Nikos';
console.log( name ) // This line will throw an error, because it is not the last statement in the file.

(
   function() {
       // Do some stuff here
    }
)();

但是如果我们将 script-2.js 更改为:

script-2.js

;(
    function() {
       // Do some stuff here
    }
)();

concatenation.js 将如下所示:

var name = 'Nikos';
console.log( name )

;(  // This will force the previous statement to finish.
   function() {
       // Do some stuff here
    }
)();

最后我发现了这个:

It forces the parser to treat the part following the + as an expression. This is usually used for functions that are invoked immediately, e.g.:

+function() { console.log("Foo!"); }();

Without the + there, if the parser is in a state where it's expecting a statement (which can be an expression or several non-expression statements), the word function looks like the beginning of a function declaration rather than a function expression and so the () following it (the ones at the end of the line above) would be a syntax error (as would the absense of a name, in that example). With the +, it makes it a function expression, which means the name is optional and which results in a reference to the function, which can be invoked, so the parentheses are valid.

• is just one of the options. It can also be -, !, ~, or just about any other unary operator. Alternately, you can use parentheses (this is more common, but neither more nor less correct syntactically):

(function() { console.log("Foo!"); })();
// or
(function() { console.log("Foo!"); }());

来自:https://stackoverflow.com/a/13341710/1150619