javascript var or not var, what's the difference? [duplicate]

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Possible Duplicate:

Difference between using var and not using var in JavaScript

Hi All

Declaringvar myVar;开发者_如何学C with var keyword or declaring myVar without it.

This might be a stupid question for some, but I'm in a learning process with 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.

So what's the difference between declaring a variable with or without the 'var' keyword?

Many Thanks

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If you don't use it, it might be a global variable, or in IE's case, it'll just blow up.

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. Always use var in 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, explicitly define it there.

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It's all about scoping. Technically you can omit var but consider this:

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
}