Window vs Var to declare variable [duplicate]

Answer 1

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.

Answer 2

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

Answer 3

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.

Answer 4

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

Answer 5

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.