Hei Coders,

I have a string "1+1", with javascript build in function eval() i can do eval("1+1") so the return value will be 2

But how about if i want to implement this concept to recursive function in javascript?

function evaluate(str) {

}

evaluate("1+1");
evaluate("1-1");
evaluate("1*1");
evaluate("1/1");

What i've tried are

function evaluate(str) {
  if (str.length === 0) {
    return "";
  }else{
    let angka;
    let symbol;
    for (let i = 0; i < str.length; i++) {
      if (isNaN(str[i])) {
        symbol = str[i];
        break;
      }else{
        angka = str[i]; 
      }
    }
    switch (symbol) {
      case "+": 
        return angka + evaluate(str.slice(1));
      case "-":
          return angka - evaluate(str.slice(1));
      case "/":
        return angka / evaluate(str.slice(1));
      case "*":
        return angka * evaluate(str.slice(1));
      default:
        return parseInt(str[0]) + evaluate(str.slice(1));
    }
  }
}

function evaluate(str) { 
  if (str.length === 0) {
    return ""
  }

  let numbers = "";
  let operator = "";
  let lastIndex = 0;
  for (let i = 0; i <= str.length; i++) {
        if (!isNaN(parseInt(str[i]))) {
          numbers += parseInt(str[i]);          
        }else{
          operator = str[i];
          lastIndex = i;
          break;
        }
  }

  // console.log(numbers, " " , operator , " " , lastIndex);
  lastIndex  = lastIndex < 1 ? 1 : lastIndex;
  if (operator === "+") {
    return numbers + evaluate(str.slice(lastIndex));
  }
}

function evaluate(str) {
  if (str.length === 0) {
    return 1;
  }else{
    let numbers = "";
    for (let i = 0; i <= str.length; i++) {
      if(parseInt(str[i]) >= 0){
        numbers = numbers + "+" +  str[i];
      }else{
        let lengthNumbers = numbers.length > 1 ? numbers.length : 1;
        let tempNumbers = numbers;
        numbers = "";
        return tempNumbers + evaluate(str.slice(lengthNumbers))
      }
    }
  }
}

===========

UPDATED

How nub i am :), for now this is my answer (according to the solutions below), Thanks for all

function evaluate(str) {
 if(str.match(/[*/+-]/)){
   let numbers = "";
   for (let i = 0; i < str.length; i++) {
     switch (str[i]) {
       case "+":
        return parseInt(numbers) + evaluate(str.slice(numbers.length+1))     
      case "*":
          return parseInt(numbers) * evaluate(str.slice(numbers.length+1))       
      case "/":
          return parseInt(numbers) / evaluate(str.slice(numbers.length+1))       
      case "-":
          return parseInt(numbers) - evaluate(str.slice(numbers.length+1))       
      default:
        numbers += str[i];
        break;
     }     
   }
 }else{
   return parseInt(str[0]);
 }

}
console.log(evaluate('1+2+3+4+5')) // 15
console.log(evaluate('1*2*3*4*5')) // 120
console.log(evaluate('20/4')) // 5
console.log(evaluate('20-6')) // 14

And no one work! I know eval will save my day, but in this case i need to solve this case, thanks before.

Try this code

function evaluate(str) {
  var reg = /[*/+-]/
  if(str.match(reg)){
    var temp = ''
    for(let i = 0; i < str.length; i++){
      if(str[i] === '+') {
        return parseInt(temp) + evaluate(str.substring(i+1))
      }
      else if(str[i] === '-') {
        return parseInt(temp) - evaluate(str.substring(i+1))
      }
      else if(str[i] === '*') {
        return parseInt(temp) * evaluate(str.substring(i+1))
      }
      else if(str[i] === '/') {
        return parseInt(temp) / evaluate(str.substring(i+1))
      }
      else {
        temp += str[i]
      }
    }
  }
  else {
    return parseInt(str)
  }
}

console.log(evaluate('1+2+3+4+5')) // 15
console.log(evaluate('1*2*3*4*5')) // 120
console.log(evaluate('20/4')) // 5
console.log(evaluate('20-6')) // 14