A simple method to format/mask numbers or any text in JavaScript.

Readme.md

Here's a demo if you wanna play with it:

https://codepen.io/moinism/pen/PoGXrdj?editors=1010

P.S: It's just a simple and lazy implementation, could be made more generalized.

P.P.S: It does not mask the input. It's just a method which can be used anywhere.

number-format.js

/*
  Usage Example:
    format('xxxx-xxxx', 12345678, '-') // outputs: 1234-5678
*/

/**
 * 
 * @param {String} mask 
 * @param {Number} number 
 * @param {String} delimeter 
 * 
 * @returns {String}
 */

function format(mask, number, delimeter) {
  if (!number) return mask;

  delimeter = delimeter || "-";

  let count = 0;
  const numberString = number.toString();
  return mask
    .split(delimeter)
    .map((group) =>
      group.replace(/x/g, (match) => { // change 'x' to any other char if needed
        return numberString.charAt(count++) || match;
      })
    )
    .join(delimeter);
}