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问题描述

我正在努力提高我对 javascript 中全局命名空间的理解,我对以下几点感到好奇:

  1. 是否有一个GOD"(即父)对象,所有对象(因为除了原始对象之外的所有事物都是对象)都可以回答,如果有,该对象是否会是窗口"?

    李>
  2. 为什么在全局级别上有变量/函数是个坏主意?

  3. 如果在全局范围内拥有变量/函数真的是个坏主意,那么闭包是避免这种情况的最佳方法吗?示例:

    函数父(){var x = 'some value';//这个 var 将被认为对所有子函数都是全局的,但不在真正的全局命名空间中函数 child1(){x.someMethod()}功能孩子2(){x*某事;}函数 child3(){x+=某事;孩子2()孩子1()}孩子3()}父母()

解决方案
  1. 是否有一个(即父母)对象?

    是的. 从技术上讲,它是所有这些原语的成员的全局对象;只是碰巧在浏览器中,window 对象 全局对象.

    >window.String === 字符串;真的

  2. 为什么在全局级别上有变量/函数是个坏主意?

    因为如果您要添加大量第 3 方库/脚本,它们都共享同一个全局对象,因此可能会发生名称冲突.这是所有使用 $ 作为别名的库(jQuery、Prototype 等)的现实问题.

  3. 如果在全局范围内拥有变量/函数真的是个坏主意,那么闭包是避免这种情况的最佳方法吗?

    x 不应被视为全局.它是通过在 parent() 函数中声明子函数而形成的闭包的一部分.您的代码段的 problem 部分是 parent() 是全局的;如果其他代码重新声明 parent() 会发生什么?这样会更好:

    (function () {函数父(){var x = '某个值';函数 child1(){x.someMethod()}功能孩子2(){x*某事;}函数 child3(){x+=某事;孩子2()孩子1()}孩子3()}父母()}());

    x 可以在子函数中访问这一事实还不错;你应该自己编写这些函数,所以你应该意识到x的存在.请记住,如果您在这些子函数中使用 var 重新声明 x,则不会影响 parent 中的 x().

I'm trying to improve my understanding of the global namespace in javascript and I'm curious about a few things:

  1. is there a "GOD" (i.e. a parent) object that all objects (since all things except primitives are objects) to answer to and if so would that object be "window" ?

  2. why is it bad idea to have vars/functions on a global level?

  3. if it is really a bad idea to have vars/functions in global scope then would closures be the best way to avoid this? example:

    function parent(){
        var x = 'some value';//this var would be considered global to all children functions but not in the true global namespace
        function child1(){
            x.someMethod()
        }
        function child2(){
            x*something;
        }
        function child3(){
            x+=something;
            child2()
            child1()
        }
        child3()
    }
    parent()
    

解决方案
  1. Yes. More technically, it's the global object that all these primitives are members of; it just happens that in the browser, the window object is the global object.

    > window.String === String;
    true
    

  2. Because if you're adding lots of 3rd party libraries/ scripts, they all share the same global object, there's the chance of name collisions. This is a real life problem with all the libraries which use $ as an alias (jQuery, Prototype and more).

  3. x shouldn't be considered global. It's part of the closure formed by declaring the child functions inside the parent() function. The problem part of your snippet is that parent() is global; what happens if some other code re-declared parent()? This would be better:

    (function () {
    
    function parent(){
        var x = 'some value';
        function child1(){
            x.someMethod()
        }
        function child2(){
            x*something;
        }
        function child3(){
            x+=something;
            child2()
            child1()
        }
        child3()
    }
    parent()
    
    }());
    

    The fact x is accessible within the child functions isn't bad; you should have written those functions yourself, so you should be aware of the existence of x. Bear in mind that if you re-declare x within those child functions with var, you won't affect the x in parent().

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08-22 13:33