closures - Javascript 模块模式和闭包

Question

我正在尝试了解 Javascript 中的模块模式，并且遇到了各种不同的方式，我可以看到这样做。以下内容之间有什么区别(如果有的话):

Person = function() {
    return {
        //...
    }
};
person1 = Person();

function Person2() {
    return {
        //...
    }
}
person2 = Person2();


person3 = function() {
    return {
        //...
    }
}();

person4 = (function() {
    return {
        // ...
    }
})();

person5 = (function() {
    return {
        // ...
    }
}());

他们似乎都对我做同样的事情。

Answer 1

// This creates a function, which then returns an object.
// Person1 isn't available until the assignment block runs.
Person = function() {
    return {
        //...
    }
};
person1 = Person();


// Same thing, different way of phrasing it.
// There are sometimes advantages of the
// two methods, but in this context they are the same.
// Person2 is available at compile time.
function Person2() {
    return {
        //...
    }
}

person2 = Person2();


// This is identical to 'person4'
// In *this* context, the parens aren't needed
// but serve as a tool for whoever reads the code.
// (In other contexts you do need them.)
person3 = function() {
    return {
        //...
    }
}();


// This is a short cut to create a function and then execute it,
// removing the need for a temporary variable.
// This is called the IIFE (Immediate Invoked Function Expression)
person4 = (function() {
    return {
        // ...
    }
})();


// Exactly the same as Person3 and Person4 -- Explained below.
person5 = (function() {
    return {
        // ...
    }
}());

在上面的上下文中，

• =函数() {}();
• = (函数() {}());
• = (函数() {})();

所有人都做同样的事情。

我会分解它们。

function() {}();
<functionExpression>(); // Call a function expression.

(<functionExpression>()); // Wrapping it up in extra parens means nothing.
// Nothing more than saying (((1))) + (((2)))


(<functionExpression>)(); 
// We already know the extra parens means nothing, so remove them and you get
<functionExpression>();  // Which is the same as case1

现在，所有这些都说明了 == 为什么有时需要括号？

因为这是一个*函数语句)

function test() {};

为了构造一个函数表达式，你需要在它之前加上某种运算符。

(function test() {})
!function test() {}
+function test() {}

所有工作。

通过对括号进行标准化，我们能够:

• 从 IIFE 中返回一个值
• 使用一致的方式让代码的读者知道它是 IIFE，而不是常规函数。