numberToThreeDigitArray.js

// Trying to find the best solution to the following problem:
//
// Display a large number with a small space in between steps of thousand.
// Thus => Convert a number to an array of max. three digits
// 
// E.g.
// Input: 10       Output: [10]
// Input: 1234     Output: [1, 234]
// Input: 24521280 Output: [23, 521, 280]

// Here are my attempts (all working solutions)

// The first "make it work without thinking much"-version
const numberToThreeDigitArray = (number) => {
  const numberStr = number.toString();

  let threeDigitSequences = [];
  let threeDigits = [];

  for (let i = numberStr.length - 1; i >= 0; i--) {
    threeDigits = [numberStr[i]].concat(threeDigits);

    if ((numberStr.length - i) % 3 === 0) {
      threeDigitSequences = [threeDigits.join('')].concat(threeDigitSequences)
      threeDigits = [];
    }

    // Final push
    if (i === 0 && threeDigits.length > 0)
      threeDigitSequences = [threeDigits.join('')].concat(threeDigitSequences)
  }

  return threeDigitSequences;
};

// The "think a little before doing"-version
const numberToThreeDigitArray = (number) => {
  if (number / 1000 < 1) return [number];

  return [
    ...numberToThreeDigitArray(Math.floor(number / 1000)),
    number % 1000
  ];
};

// The third "why don't we do string iteration"-version
const numberToThreeDigitArray = (number) => {
  return number.toString().split('').reverse().map((char, i) => {
    return i !== 0 && i % 3 === 0
      ? ' ' + char
      : char;
  }).join('').split('').reverse().join('').split(' ');
}

// => Not really happy with either solution yet, but so far I prefer solution 2