在最基本的层面上， return 关键字定义了函数应返回的内容。所以如果我有这个功能：

On the most basic level, the return keyword defines what a function should return. So if I have this function:

function foo() { return 4; }

然后调用它：

var bar = foo();

foo（）将返回 4 ，因此现在 bar 的值也是 4 。

foo() will return 4, hence now the value of bar is also 4.

根据您的具体示例：

在此用例中，返回用于基本上限制对哈希变量内部变量的外部访问。

In this use case the return is used to basically limit outside access to variables inside the hash variable.

任何写成的函数如下：

Any function written like so:

(function() {...})();

是自我调用，这意味着它会立即运行。通过将 hash 的值设置为自调用函数，这意味着代码可以尽快运行。

Is self-invoking, which means it runs immediately. By setting the value of hash to a self-invoking function, it means that code gets run as soon as it can.

该函数然后返回以下内容：

That function then returns the following:

return {         
    contains: function(key) {
        return keys[key] === true;         
    },
    add: function(key) { 
        if (keys[key] !== true){
            keys[key] = true;             
        }
    }     
};

这意味着我们可以访问包含和添加函数如下：

This means we have access to both the contains and add function like so:

hash.contains(key);
hash.add(key);

在哈希里面，还有一个变量 keys 但是 hash 设置为自调用函数不返回，因此我们无法访问 key 在哈希之外，所以这不起作用：

Inside hash, there is also a variable keys but this is not returned by the self-invoking function that hash is set to, hence we cannot access key outside of hash, so this wouldn't work:

hash.keys //would give undefined

它本质上是一个构造代码的方法，可以通过使用JavaScript闭包来创建私有变量。有关详细信息，请查看此帖子： http://net.tutsplus.com/tutorials/javascript-ajax/quick-tip-private-variables-in-javascript/

It's essentially a way of structuring code that can be used to create private variables through the use of JavaScript closures. Have a look at this post for more information: http://net.tutsplus.com/tutorials/javascript-ajax/quick-tip-private-variables-in-javascript/

希望这有助于：）

杰克。