var关键字的目的是什么？何时应使用（或省略）？

问题：

NOTE : This question was asked from the viewpoint of ECMAScript version 3 or 5. The answers might become outdated with the introduction of new features in the release of ECMAScript 6. 注意 ：从ECMAScript版本3或5的角度提出了此问题。随着ECMAScript 6版本中引入新功能，答案可能会过时。

What exactly is the function of the var keyword in JavaScript, and what is the difference between JavaScript中var关键字的功能到底是什么，它们之间有什么区别

var someNumber = 2;
var someFunction = function() { doSomething; }
var someObject = { }
var someObject.someProperty = 5;

and 和

someNumber = 2;
someFunction = function() { doSomething; }
someObject = { }
someObject.someProperty = 5;

? ？

When would you use either one, and why/what does it do? 您什么时候会使用其中一个？为什么/会做什么？

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解决方案：

参考一： https://stackoom.com/question/6AXY/var关键字的目的是什么-何时应使用-或省略
参考二： https://oldbug.net/q/6AXY/What-is-the-purpose-of-the-var-keyword-and-when-should-I-use-it-or-omit-it

来源：oschina

链接：https://my.oschina.net/u/3797416/blog/4478971