If you’re in the global scope then there’s not much difference. Read Kangax’s answer for explanation
If you’re in a function then var
will create a local variable, “no var” will look up the scope chain until it finds the variable or hits the global scope (at which point it will create it):
// These are both globals
var foo = 1;
bar = 2;
function()
{
var foo = 1; // Local
bar = 2; // Global
// Execute an anonymous function
(function()
{
var wibble = 1; // Local
foo = 2; // Inherits from scope above (creating a closure)
moo = 3; // Global
}())
}
If you’re not doing an assignment then you need to use var
:
var x; // Declare x