how can i get a 4 at the second console.log?

function sumDigits(num) {
    var sNumber = num.toString();
    var acc = 0;
    var i = 0;
    While(i < sNumber.length) {
        if (sNumber[i] === "-") {
            acc = Number(sNumber[2]) - Number(sNumber[1]);
            i = 3;
        } else {
            acc += Number(sNumber[i]);
            i = i + 1;
        }
    }
    return acc;
}

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console.log(sumDigits(1148));
console.log(sumDigits(-316));

function sumDigits(num) {
  var sNumber = num.toString();
  var acc = 0;
  for(var i = 0; i < sNumber.length; i ++){   
    var number;
    if (sNumber.charAt(i) === "-")
    {
    i++;
    number = Number("-" + sNumber.charAt(i));
    }
    else
    {
    number = Number(sNumber.charAt(i));
    }
    acc += number;  
  }
  return acc;
}

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<script>
function sumDigits(dig)
{
  var atorstack = [];
  var andstack = [];
  var n = dig.toString();
  for(var i = 0; i < n.length; i++) {
    if (n[i].match(/[\+-]/)) {
      atorstack.push(n[i]);
    }
    else {
      if (andstack.length == 0) {
        andstack.push(n[i]);
      }
      else {
        var op = atorstack.pop() || '+';
        var and = andstack.pop();
        var result = eval(n[i] + op + and);
        andstack.push(result);
      }
    }
  }
  var ator = atorstack.pop() || '';
  return parseInt(ator + andstack.pop());
}

console.log(sumDigits(-316));
console.log(sumDigits(-3+1-6));

</script>

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