String left pad.

leftPad.js

export const leftPad = (str, howMany, char = '0') => {
  if(str.length >= howMany) return str;

  const space = Array(howMany).fill(char);
  const aStr = str.split('');
  const merge = space.concat(aStr);
  merge.splice(0, aStr.length);

  return merge.join('');
}