Simplest inline method to left pad a string [duplicate]

Possible Duplicate:
Is there a JavaScript function that can pad a string to get to a determined length?

What's the simplest way to left pad a string in javascript?

I'm looking for an inline expression equivalent to mystr.lpad("0", 4): for mystr='45' would return 0045.

Found a simple one line solution:

("0000" + n).slice(-4)

If the string and padding are in variables, you would have:

mystr = '45'
pad = '0000'
(pad + mystr).slice(-pad.length)

Answer found here, thanks to @dani-p. Credits to @profitehlolz.

function pad(value, length) {
    return (value.toString().length < length) ? pad("0"+value, length):value;
}