Compare two last character in a string

Question

I am programming a calculator in AngularJS. I am stuck on a validating user input. I do not want the user to be able to enter two 2 operators (\'+\',\'/\',\'*\') next to each ot

Answer 1

There were two things wrong.

1. $scope.expression.length > 3 should have been $scope.expression.length > 2
2. You were calling $scope.expression += String(ope); twice

I made a minor change below so I could run it in the code snippet window.

I also added subtraction to liste.

var $scope = {
  expression: ""
};


var liste = ['+', '/', '*', '-'];

debugger
$scope.add = function (ope) {
  var temp = $scope.expression + String(ope);
  console.log(temp);
  var len = temp.length - 1;

  if (len > 1) {
    var der = temp[len];
    var avantDer = temp[len - 1];

    if (liste.includes(der) && liste.includes(avantDer)) {
      console.log("error");
    } else {
      $scope.expression = temp;
    }
  }
  else {
    $scope.expression = temp;
  }
};

$scope.add('3');
$scope.add('+');
$scope.add('-');

When I call $scope.add('-'); it displays the error like you expect.