const e = '3 4 2 * 1 5 - 2 3 ^ ^ / +';
const s = [], tokens = e.split(' ');
for (const t of tokens) {
  const n = Number(t);
  if (!isNaN(n)) {
    s.push(n);
  } else {
    if (s.length < 2) {
      throw new Error(`${t}: ${s}: insufficient operands.`);
    }
    const o2 = s.pop(), o1 = s.pop();
    switch (t) {
      case '+': s.push(o1 + o2); break;
      case '-': s.push(o1 - o2); break;
      case '*': s.push(o1 * o2); break;
      case '/': s.push(o1 / o2); break;
      case '^': s.push(Math.pow(o1, o2)); break;
      default: throw new Error(`Unrecognized operator: [${t}]`);
    }
  }
  console.log(`${t}: ${s}`);
}

if (s.length > 1) {
  throw new Error(`${s}: insufficient operators.`);
}