javascript var 或 not var，有什么区别？
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javascript var or not var, what's the difference?
提问by Shaoz
Possible Duplicate:
Difference between using var and not using var in JavaScript
Hi All
大家好
Declaringvar myVar;with varkeyword or declaring myVarwithout it.
var myVar;使用var关键字声明或myVar不使用关键字声明。
This might be a stupid question for some, but I'm in a learning process with javascript.
对于某些人来说，这可能是一个愚蠢的问题，但我正在学习 javascript。
Sometime, when reading other people's code, I see that some variables are declared without the 'var' at the front. Just to emphasise, these variables are not even declared as parameters of a function.
有时，在阅读其他人的代码时，我看到某些变量的声明没有前面的“var”。只是强调一下，这些变量甚至没有被声明为函数的参数。
So what's the difference between declaring a variable with or without the 'var' keyword?
那么声明一个带有或不带有 'var' 关键字的变量有什么区别呢？
Many Thanks
非常感谢
回答by Nick Craver
If you don't use it, it mightbe a global variable, or in IE's case, it'll just blow up.
如果你不使用它，它可能是一个全局变量，或者在 IE 的情况下，它会爆炸。
There are cases you don't need it, for example if it's a parameter to the function you're in, it's already declared. Alwaysuse varin any other cases (other cases being: unless you're manipulating a variable that already exists). No matter what scope it needs to be defined at, explicitlydefine it there.
在某些情况下您不需要它，例如，如果它是您所在函数的参数，则它已被声明。 始终使用var在任何其他情况下（其他情况是：除非你操纵已经存在的变量）。不管它需要在什么范围内定义，在那里明确定义它。
回答by Ollie Edwards
It's all about scoping. Technically you can omit var but consider this:
这都是关于范围界定的。从技术上讲，您可以省略 var 但请考虑：
myVar = "stuff";
function foo() {
myVar = "junk"; //the original myVar outside the function has been changed
}
function bar() {
var myVar = "things" //A new scoped myvar has been created internal to the function
}
