/**
 * @param num A number in the int32 range [-2147483648 .. 2147483647]
 * @returns A number[] containing each digit of `num`.
 * If negative `num` given, resulting array will contain negatives numbers.
 */
function separateDigits(num: number): number[] {
  let arr: number[] = [];
  let lastDigit: number;

  num = toInt32(num);

  do {
    lastDigit = num % 10;
    arr.push(lastDigit);
    // Updating num to num/10 cuts off the last digit:
    num = toInt32(num / 10);
  }
  while (num !== 0);

  return arr.reverse();
}

/**
* Fast bitwise operation, truncates floating point number resulting in int32.
* The >> bitwise operator is used, an overflow occurs if number too large.
* A *safe* integer division in JavaScript would be Math.floor(x/y);
* @param f A (JavaScript) number between [-2147483648.999 .. 2147483647.999]
* @returns Input 'f' truncated to Int32.
*/
function toInt32(f: number): number {
  // Note that type "number" in JS is always "float" internally.
  return f >> 0;
}

console.log(separateDigits(3142520));

// Output:
// [3, 4, 1, 2, 5, 2, 0]