leftPad, rightPad, oh whatever.

pad.js

const pad = (leftOrRight = 'left') => maxLength => char => value => {
  const strValue = typeof value === 'number' ? value.toString() : value;
  if (strValue.length >= maxLength) {
    return strValue;
  }
  if (typeof maxLength !== 'number') {
    throw new Error('maxLength should be a number');
  }

  const padding = Array(maxLength - strValue.length)
    .fill(char)
    .join('');

  return leftOrRight === 'left' ? `${padding}${strValue}` : `${strValue}${padding}`;
};

const leftPad = pad();
const leftPadTwo = leftPad(2);
const leftPadTwoZero = leftPadTwo('0');
const leftPadTwoSpace = leftPadTwo(' ');
console.log(leftPadTwoZero(8)); // '08'
console.log(leftPadTwoSpace(8)); // ' 8'

const rightPad = pad('right');
const rightPadFour = rightPad(4);
const rightPadFourAsterisk = rightPadFour('*');
const rightPadFourSpace = rightPadFour(' ');
console.log(rightPadFourAsterisk(8)); // '8***'
console.log(rightPadFourSpace(8)); // '8   '