Number function in javascript : number function in javascript can be used to multiply,divide,find remainder but cannot be used for subtraction and addition.
    var theNumber = Number ( prompt (" Pick a number " , "") ) ;
    alert ("  difference  " +
    theNumber - theNumber ) ;
    // -> difference NaN 
    why not 0?
    var theNumber = Number ( prompt (" Pick a number " , "") ) ;
    alert ("  sum  " +
    theNumber + theNumber ) ;
    // ->3
    // ->33
why is concatenation occurring? why not 6?
please help! 
