为什么将javascript名称空间作为函数? [英] Why base a javascript namespace as a function?

问题描述

我正在阅读一个库的源代码，该库必须保持匿名，并且我看到它正在使用一个空函数来设置名称空间.它似乎与对象文字符号(OLN)相似，只是基数是一个函数.

I was reading the source code of a library, which must remain anonymous, and I see that it's using an empty function to setup the namespace. It appears to be similar to the object literal notation (OLN) except that the base is a function.

这是声明的示例.

/**
 * Base namespace for FOO library
 * @name FOO
 * @namespace
 */
function FOO(){}

FOO.bar = 'bar const..';
FOO.fooFunc = function () { /* code */ };
FOO.Bar = function () { /* some constructor */ };
FOO.Bar.prototype.baz = function () { /* A prototype method on FOO.Bar */ };
...

如您所见，FOO名称空间是一个空函数.是否有必要将命名空间声明为空函数?这是对OLN模式的滥用吗?看来这可能是工厂模式的开始.名称空间上没有原型方法(例如FOO.prototype.bar = ...).显然，调用FOO()不会执行任何操作.有人认出这种模式吗?

As you can see, the FOO namespace is an empty function. Is there any point of declaring the namespace as an empty function? Is this a misuse of the OLN pattern? It looks like it may have been the start of a factory pattern. There's no prototype methods on the namespace (e.g. FOO.prototype.bar = ...). Calling FOO() clearly does nothing. Does anyone recognize this pattern?

推荐答案

命名函数为 悬挂 -有效地移至其封闭范围的顶部.使用命名函数可以允许在声明名称空间之前进行赋值:

Named functions are hoisted - effectively moved to the top of their enclosing scope. Using a named function could allow assignment before the namespace is declared:

FOO.bar = "bar";
function FOO() {}
console.log(FOO.bar); // bar

与Object文字(或未命名的函数)相比:

Compared to an Object literal (or non-named function):

FOO.bar = "bar";
var FOO = {};
console.log(FOO.bar); // undefined

任何人不太可能计划将成员分配到这样的命名空间，但这可能会发生.

It's unlikely that anybody would plan to assign members to a namespace like this, but it could happen.

我能想到的唯一另一个优点是，函数可以具有一个固有的名称，这可能对调试很有用.

The only other advantage I can think of a is that functions can have an inherent name, which may be useful for debugging.

例如，如果名称空间成员具有namespace属性(他们可能没有):

For example, if namespace members had a namespace property (which they probably don't):

function FOO(){}
FOO.bar = { namespace: FOO };
console.log(FOO.bar.namespace); // function FOO(){}

相比:

var FOO = {};
FOO.bar = { namespace: FOO };
console.log(FOO.bar.namespace); // Object {bar: Object}

纯粹的推测:某些名称空间也可能使用这样的函数进行初始化.这可能是一个名称空间的示例，该名称空间不需要任何初始化，但是选择使用函数来保持一致性.

Pure speculation: it's also possible that some namespaces could use a function like this for initialisation. This could be an example of a namespace that does not need any initialisation, but chooses to use a function for consistency.

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