Zero-padding a number to have six digits

Question

This is a switch statement in JavaScript. I have a feeling that it can be done in a shorter way.

switch(n.length){
  case 1:
    n = '00000' + n;
  break;
  case 2:
    n = '0000' + n;
  break;
  case 3:
    n = '000' + n;
  break;
  case 4:
    n = '00' + n;
  break;
  case 5:
    n = '0' + n;
  break;
}

Answer 1

function foobar(n)
{
    var zeroes = "000000";
    return zeroes.substr(n.length) + n.toString();
}

Answer 2

Well, the value of n is known in each case, so you can just put it in the string:

switch(n) {
  case 1:
    n = '000001';
  break;
  case 2:
    n = '00002';
  break;
  case 3:
    n = '0003';
  break;
  case 4:
    n = '004';
  break;
  case 5:
    n = '05';
  break;
}

If n can only have one of these values, you can use it as index in an array:

n = ['000001','00002','0003','004','05'][n - 1];

Edit:

With the edited code (using n.length in the switch), it would be:

n = ['00000','0000','000','00','0'][n.length - 1] + n;

Answer 3

It seems you're trying to implement part of the functionality of printf. Use one of the existing implementations, e.g. dive.into.javascripts sprintf to do the zero-padding:

n = sprintf("%06d", n);

Answer 4

Currently the other answers do not provide a robust way of doing this. They either use magic numbers or create long strings of zeroes manually. So I am adding this answer as a reference for anyone visiting this question in the future.

We can create the padding by joining an empty array together. I have provided two options: straight code or a function for reuse.

Straight Code:

var desiredLength = 6;

if (n.length < desiredLength) {
   n = Array(desiredLength - n.length + 1).join("0") + n;
}

Function:

function padTo(length, str, ch) {
   if (str.length < length) {
      return Array(length - str.length + 1).join(ch) + str;
   }

   return str;
} 

// Usage
padTo(6, "3", "0")); // 000003