const calcNumbers = (num1, num2, sign) => {
  switch(sign) {
    case '+': 
      return num1 + num2;
      break;
    case '-': 
      return num1 - num2;
      break;    
    case '/': 
      return num1 / num2;
      break;
    case '*': 
      return num1 / num2;
      break; 
  }
};

const extractSign = (str) => {
  const signs = ['+', '-', '/', '*']
  let sign
  for (char of str) {
    if (signs.includes(char)) {
      sign = char;
    }
  }
  return sign;
};

const input = "4 /2";

console.log(calcNumbers(+input[0], +input[input.length - 1], extractSign(input)))

const calcNumbers = ([num1, sign, num2]) => {
  switch (sign) {
    case "+":
      return num1 + num2;
      break;
    case "-":
      return num1 - num2;
      break;
    case "/":
      return num1 / num2;
      break;
    case "*":
      return num1 * num2;
      break;
  }
};

const extractParticles = (str) => {
  const signs = ["+", "-", "/", "*"];
  const numbers = [];
  let sign = "";

  for (char of str) {
    if (signs.includes(char)) {
      sign = char;
    } else if (char !== ' ' && typeof +char === "number") {
      numbers.push(char);
    }
  }
  return [+numbers[0], sign, +numbers[1]];
};

const input = "2 *2";

console.log(calcNumbers(extractParticles(input)));