no-operator-multiply.js

function incrementInt(num) {
  switch(+num) {
    case 0:
      return [1, 0];
    case 1:
      return [2, 0];
    case 2:
      return [3, 0];
    case 3:
      return [4, 0];
    case 4:
      return [5, 0];
    case 5:
      return [6, 0];
    case 6:
      return [7, 0];
    case 7:
      return [8, 0];
    case 8:
      return [9, 0];
    case 9:
      return [0, 1];
  }
}
function decrementInt(num) {
  switch(+num) {
    case 0:
      return [9, 1];
    case 1:
      return [0, 0];
    case 2:
      return [1, 0];
    case 3:
      return [2, 0];
    case 4:
      return [3, 0];
    case 5:
      return [4, 0];
    case 6:
      return [5, 0];
    case 7:
      return [6, 0];
    case 8:
      return [7, 0];
    case 9:
      return [8, 0];
  }
}
function increment(numInt, total = []) {
  const num = String(numInt).split('');
  if (num.length === 0) return combine(total);
  const inc = incrementInt(num.at(-1));
  if (!inc[1]) return combine([...num.slice(0, -1), inc[0], ...total]);
  else {
    if (num.slice(0, -1).length === 0) {
      return combine([String(increment(combine([0]), [...total, inc[0]]))]);
    }
    return combine([String(increment(combine(num.slice(0, -1)), [...total, inc[0]]))]);
  }
}
function decrement(numInt, total = []) {
  const num = String(numInt).split('');
  if (num.length === 0) return combine(total);
  const dec = decrementInt(num.at(-1));
  if (!dec[1]) return combine([...num.slice(0, -1), dec[0], ...total]);
  else {
    if (num.slice(0, -1).length === 0) {
      return combine([String(decrement(combine([]), [...total, dec[0]]))]);
    }
    return combine([String(decrement(combine(num.slice(0, -1)), [...total, dec[0]]))]);
  }
}
function combine(numArr) {
  return +numArr.join('');
}
function add(num1, num2) {
  if (num2 == 0) return num1;
  return add(increment(num1), decrement(num2));
}
function subtract(num1, num2, neg = false) {
  if (num2 == 0) {
    if (neg) {
      return -num1;
    }
    return num1;
  };
  if (num1 == 0) neg = true;
  return subtract(!neg ? decrement(num1) : increment(num1), decrement(num2), neg);
}
function multiply(num1, num2, acc = '') {
  if (num2 == 0) {
    return acc;
  }
  return multiply(num1, decrement(num2), add(num1, acc));
}


(() => {
  const m1 = process.argv[2];
  const m2 = process.argv[3];

  let neg = false;
  if (m1 == 0 || m2 == 0) {
    console.log(0);
    return;
  }
  if (m1 == 1) {
    console.log(m2);
    return;
  }
  if (m2 == 1) {
    console.log(m1);
    return;
  }
  if ((m1 < 0 && m2 > 0) || (m2 < 0 && m1 > 0)) {
    neg = true;
  }

  console.log(`${neg ? '-' : ''}${multiply(Math.abs(m1), Math.abs(m2))}`);
})();