Pad a number with leading zeros in JavaScript [dup

Question

Possible Duplicate:
How can I create a Zerofilled value using JavaScript?

In JavaScript, I need to have padding.

For example, if I have the number 9, it will be "0009". If I have a number of say 10, it will be "0010". Notice how it will always contain four digits.

One way to do this would be to subtract the number minus 4 to get the number of 0s I need to put.

Is there was a slicker way of doing this?

Answer 1

You did say you had a number-

String.prototype.padZero= function(len, c){
    var s= '', c= c || '0', len= (len || 2)-this.length;
    while(s.length<len) s+= c;
    return s+this;
}
Number.prototype.padZero= function(len, c){
    return String(this).padZero(len,c);
}

Answer 2

For fun, instead of using a loop to create the extra zeros:

function zeroPad(n,length){
  var s=n+"",needed=length-s.length;
  if (needed>0) s=(Math.pow(10,needed)+"").slice(1)+s;
  return s;
}

Answer 3

Funny, I recently had to do this.

function padDigits(number, digits) {
    return Array(Math.max(digits - String(number).length + 1, 0)).join(0) + number;
}

Use like:

padDigits(9, 4);  // "0009"
padDigits(10, 4); // "0010"
padDigits(15000, 4); // "15000"

Not beautiful, but effective.