1

JS代码

    var foo = "Hello World!"; // <------- global scope
    document.write("<p>Before our anonymous function foo means '" + foo + '".</p>');

    (function() {
        // The following code will be enclosed within an anonymous function
        var foo = "Goodbye World!"; // <------- local scope
        document.write("<p>Inside our anonymous function foo means '" + foo + '".</p>');
    })(); // We call our anonymous function immediately

    document.write("<p>After our anonymous function foo means '" + foo + '".</p>');

HTML 输出

Before our anomymous function foo means 'Hello World!".

Inside our anomymous function foo means 'Goodbye World!".

After our anomymous function foo means 'Hello World!".

我的问题是

  • 当我们替换foo函数内部变量的值时，为什么不替换它？它如何仍然包含"Hello World!"?
  • 如果我要访问函数内部的全局变量，我该怎么做？
4

3 回答 3

3

通过var foo在函数内部使用，您明确告诉变量仅在该函数内进行本地更改。如果要全局更改它，只需使用foo = ...

如果你想阅读它，我建议这个 SO Question

于 2013-02-07T17:30:43.260 回答
1

从匿名函数中删除var语句，您将更改全局变量：

var foo = "Hello World!"; // <------- global scope
document.write("<p>Before our anonymous function foo means '" + foo + '".</p>');

(function() {
    // The following code will be enclosed within an anonymous function
    foo = "Goodbye World!"; // <------- local scope
    document.write("<p>Inside our anonymous function foo means '" + foo + '".</p>');
})(); // We call our anonymous function immediately

document.write("<p>After our anonymous function foo means '" + foo + '".</p>');
于 2013-02-07T17:30:32.030 回答
0

您正在使用函数作用域变量来隐藏全局变量。要访问全局变量，您可以使用 window.foo 明确说明

var foo = "Hello World!"; // <------- global scope
document.write("<p>Before our anonymous function foo means '" + foo + '".</p>');

(function() {
    // The following code will be enclosed within an anonymous function
    var foo = "Goodbye World!"; // <------- local scope
    document.write("<p>Inside our anonymous function foo means '" + foo + '".</p>');
    document.write("<p>Inside our anonymous function window.foo means '" + window.foo + '".</p>');
    window.foo = window.foo + foo;
})(); // We call our anonymous function immediately

document.write("<p>After our anonymous function foo means '" + foo + '".</p>');

这将打印“Hello World！再见世界！”

于 2013-02-07T17:38:00.157 回答