了解 javascript 全局命名空间和闭包

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()

1. <块引用>

   是否有一个神(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 对象是 全局对象.

   <代码>>window.String === 字符串；真的

2. <块引用>

   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. <块引用>

   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()
   

1. Is there a god (i.e. a parent) object?

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

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

   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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