How to Add Leading Zeros to Numbers in JavaScript?

Leading Zeros in JavaScript Numbers

In JavaScript, is there a way to automatically add leading zeros to numbers to achieve a specific string length? For instance, converting 5 to "05" with a target length of 2?

Solution:

Conversion to String

Since numbers inherently don't have leading zeros, we need to convert the number to a string first. Here's a sample function:

function pad(num, size) {
  num = num.toString();
  while (num.length < size) {
    num = "0" + num;
  }
  return num;
}

Example:

pad(5, 2); // "05"

Alternative Approach

If the maximum number of leading zeros is known, an alternative method can be more efficient:

function pad(num, size) {
  var s = "000000000" + num;
  return s.substr(s.length - size);
}

Negative Numbers

Handling negative numbers requires stripping the negative sign and re-adding it after padding:

function padWithSign(num, size) {
  if (num < 0) {
    num = -num;
    return "-" + pad(num, size);
  } else {
    return pad(num, size);
  }
}

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