[removed] What is the difference between `if (!x)` and `if (x == null)`?

Question

What is the difference between if (!x) and if (x == null); that is, when can their results be different?

Answer 1

if (!x) 

coerces x uses the internal ToBoolean function

if (x==null)

coerces both operands using the internal ToPrimitive function (which generally resolves each side to a number, occasionally a string, depending on the operands)

For full explanantion of ToBoolean vs ToPrimitive see http://javascriptweblog.wordpress.com/2011/02/07/truth-equality-and-javascript/