这样的写法 (function(){ /* do something */ })(); 的含义, JavaScript

执行匿名函数，并且匿名函数中的变量不污染全局变量空间。

代码:

<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8" />
</head>
<body>
<script type="text/javascript">
(function(){
var inside="inside";
document.writeln("函数0 无返回值，运行，未污染全局变量空间 ");
document.writeln("I am running in a function anonymous. ");
document.writeln("var inside undefined :" + (typeof inside === 'undefined') + " ");
document.writeln("var inside values: " + inside + " ");
})();
var res1 = (function () {
var inside="inside";
document.writeln("函数1 有返回值，运行，未污染全局变量空间 ");
document.writeln("I am running in a function anonymous. ");
document.writeln("var inside undefined :" + (typeof inside === 'undefined') + " ");
document.writeln("var inside values: " + inside + " ");
return 111;
})();
var res2 = function () {
var inside="inside";
document.writeln("函数2 有返回值，运行，未污染全局变量空间 ");
document.writeln("I am running in a function anonymous. ");
document.writeln("var inside undefined :" + (typeof inside === 'undefined') + " ");
document.writeln("var inside values: " + inside + " ");
return 222;
}();
var res3 = function foo() {
var inside="inside";
document.writeln("函数3 有返回值，运行，未污染全局变量空间 ");
document.writeln("I am running in a naming function. ");
document.writeln("var inside undefined :" + (typeof inside === 'undefined') + " ");
document.writeln("var inside values: " + inside + " ");
return 333;
}();
function bar() {
var inside="inside";
document.writeln("函数4 有返回值，定义未运行，未污染全局变量空间 ");
document.writeln("I am running in a naming function. ");
document.writeln("var inside undefined :" + (typeof inside === 'undefined') + " ");
document.writeln("var inside values: " + inside + " ");
return 444;
};
var res4 = bar(); // bar运行
document.writeln("全局，所有匿名函数未污染全局变量空间 ");
document.writeln("var inside undefined :" + (typeof inside === 'undefined'));
document.writeln(" ");
document.writeln("function foo undefined :" + (typeof foo === 'undefined'));
document.writeln(" ");
document.writeln("function bar undefined :" + (typeof bar === 'undefined'));
document.writeln(" ");
document.writeln("匿名函数1返回值:" + res1);
document.writeln(" ");
document.writeln("匿名函数2返回值:" + res2);
document.writeln(" ");
document.writeln("命名函数foo定义并调用的返回值:" + res3);
document.writeln(" ");
document.writeln("命名函数bar调用的返回值:" + res4);
document.writeln(" ");
</script>
</body>
</html>

执行结果:

函数0 无返回值，运行，未污染全局变量空间
I am running in a function anonymous.
var inside undefined :false
var inside values: inside
函数1 有返回值，运行，未污染全局变量空间
I am running in a function anonymous.
var inside undefined :false
var inside values: inside
函数2 有返回值，运行，未污染全局变量空间
I am running in a function anonymous.
var inside undefined :false
var inside values: inside
函数3 有返回值，运行，未污染全局变量空间
I am running in a naming function.
var inside undefined :false
var inside values: inside
函数4 有返回值，定义未运行，未污染全局变量空间
I am running in a naming function.
var inside undefined :false
var inside values: inside
全局，所有匿名函数未污染全局变量空间
var inside undefined :true
function foo undefined :true
function bar undefined :false
匿名函数1返回值:111
匿名函数2返回值:222
命名函数foo定义并调用的返回值:333
命名函数bar调用的返回值:444

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