What's the difference between variable definition and declaration in JavaScript?

Question

Is this a variable definition or declaration? And why?

var x;

..and is the memory reserved for x after this st

Answer 1

Declaring a variable is like telling the (javascript) compiler that this token x is something I want to use later. It does point to a location in memory, but it does not yet contain a value. ie. it is undefined

var x;

defining it means to give it a value which you can either do it like:

x = 10; // defining a variable that was declared previously

or like this:

var y = 20; // declaring and defining a variable altogether.

http://msdn.microsoft.com/en-us/library/67defydd(v=vs.94).aspx http://www.w3schools.com/js/js_variables.asp