testhulu.js

//////////////////////////////////////////////////////////////
//
// Question 3:
//
// Implement a basic calculator to evaluate a simple expression string.
// 
// The expression string may contain the plus +, minus sign -, 
// non-negative integers and empty spaces.
// 
// You may assume that the given expression is always valid.
// 
// Some examples:
// "1 + 1" = 2
// " 2-1 + 2 " = 3
//
// Note:
// * Do not use the eval built-in library function.
//
///////////////////////////////////////////////////////////////

function calculator(expression) {
  var operator = '';
  return Array.from(expression).reduce(function (acc, character) {
    var number = parseInt(character);
    
    if (character === ' ') {
      return acc;
    }
    
    if (isNaN(number) ) {
      operator = character;
    } else if (operator.length > 0) {
      switch(operator) {
        case '+':
          acc = acc + number;
        break;
        case '-':
          acc = acc - number;
        break;
      }
    } else {
      acc = number;
    }
    
    return acc;
  }, 0);
}

console.log(calculator("1 + 1"));
console.log(calculator(" 2-1 + 2 "));