How to Prepend Leading Zeros to Numbers in JavaScript?

Prepending Leading Zeros to Numbers in JavaScript

When working with numbers in JavaScript, there may arise a need to output them with a fixed length by prepending leading zeros. This can enhance readability and uniformity in visual displays.

Conversion to String

Numbers do not natively support leading zeros, so the first step is to convert the number to a string. This can be achieved using the toString() method:

const num = 5;
const numString = num.toString(); // "5"

Prepending Zeros

To prepend zeros, you can use string manipulation techniques. The following function achieves this using a while loop:

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

By repeatedly concatenating "0" to the beginning of the string, the function ensures that the desired number of leading zeros is added.

Alternative Approach

If the maximum number of leading zeros is known beforehand, an alternative approach is to append a large number of zeros to the beginning of the string and then trim it to the desired length:

function pad(numString, size) {
  const paddedString = "000000000" + numString;
  return paddedString.substring(paddedString.length - size);
}

Example

Using the above functions, you can easily output numbers with leading zeros:

console.log(pad(5, 3)); // "005"
console.log(pad(1234, 6)); // "001234"

Handling Negative Numbers

If you need to handle negative numbers, you can modify the pad() function to strip and re-add the negative sign accordingly.

The above is the detailed content of How to Prepend Leading Zeros to Numbers in JavaScript?. For more information, please follow other related articles on the PHP Chinese website!