JS 有名函数表达式全面解析

Example #1: Function expression identifier leaks into an enclosing scope

实例1：函数表达式标示符渗进了外围作用域

var f = function g(){};
typeof g; // "function"

Remember how I mentioned that an identifier of named function expression is not available in an enclosing scope? Well, JScript doesn't agree with specs on this one - g in the above example resolves to a function object. This is a most widely observed discrepancy. It's dangerous in that it inadvertedly pollutes an enclosing scope - a scope that might as well be a global one - with an extra identifier. Such pollution can, of course, be a source of hard-to-track bugs.

我刚才提到过一个有名函数表达式的标示符不能在外部作用域中被访问。但是，JScript在这点上和标准并不相符，在上面的饿例子中g却是一个函数 对象。这个是一个可以广泛观察到的差异。这样它就用一个多余的标示符污染了外围作用域，这个作用域很有可能是全局作用域，这样是很危险的。当然这个污染可 能是一个很难去处理和跟踪的bug的根源
Example #2: Named function expression is treated as BOTH - function declaration AND function expression

实例2：有名函数表达式被进行了双重处理，函数表达式和函数声明

typeof g; // "function"
var f = function g(){};

As I explained before, function declarations are parsed foremost any other expressions in a particular execution context. The above example demonstrates how JScript actually treats named function expressions as function declarations. You can see that it parses g before an “actual declaration” takes place.

正如我前面解释的，在一个特定的执行环境中，函数声明是在所有的表达式之前被解释。上面的例子说明JScript实际上把有名函数表达式作为一个函 数声明来对待。我们可以看到他在一个实际的声明之前就被解释了。

This brings us to a next example:

在此基础上我们引入了下面的一个例子。
Example #3: Named function expression creates TWO DISCTINCT function objects!

实例3：有名函数表达式创建两个不同的函数对象。

var f = function g(){};
f === g; // false

f.expando = 'foo';
g.expando; // undefined

This is where things are getting interesting. Or rather - completely nuts. Here we are seeing the dangers of having to deal with two distinct objects - augmenting one of them obviously does not modify the other one; This could be quite troublesome if you decided to employ, say, caching mechanism and store something in a property of f, then tried accessing it as a property of g, thinking that it is the same object you're working with.

在这里事情变得更加有趣了，或者是完全疯掉。这里我们看到必须处理两个不同的对象的危险，当扩充他们当中的一个的时候，另外一个不会相应的改变。如 果你打算使用cache机制并且在f的属性中存放一些东西，只有有试图在g的属性中访问，你本以为他们指向同一个对象，这样就会变得非常麻烦