Window vs Var to declare variable [duplicate]

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Possible Duplicate:

Difference between using var and not using var in JavaScript

Should I use window.variable or var?

I have seen two ways to declare a class in javascript.

like

window.ABC = ....

or

var ABC = ....

Is there any difference in terms of using the class/ variable?

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window.ABC scopes the ABC variable to window scope (effectively global.)

var ABC scopes the ABC variable to whatever function the ABC variable resides in.

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var creates a variable for the current scope. So if you do it in a function, it won't be accessible outside of it.

function foo() {
    var a = "bar";
    window.b = "bar";
}

foo();
alert(typeof a); //undefined
alert(typeof b); //string
alert(this == window); //true

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window.ABC = "abc"; //Visible outside the function
var ABC = "abc"; // Not visible outside the function.

If you are outside of a function declaring variables, they are equivalent.

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window makes the variable global to the window. Unless you have a reason for doing otherwise, declare variables with var.

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The major difference is that your data is now attached to the window object instead of just existing in memory. Otherwise, it is the same.