javascript function no return code example

Example: js function

function myfunction() {
  console.log("function");
};

myfunction() //Should say "function" in the console.

function calculate(x, y, op) {
  var answer;
  if ( op = "add" ) {
    answer = x + y;
  };
  else if ( op = "sub" ) {
    answer = x - y;
  };
  else if ( op = "multi" ) {
    answer = x * y;
  };
  else if ( op = "divide" ) {
    answer = x / y;
  };
  else {
    answer = "Error";
  };
  return answer;
};

console.log(calculate(15, 3, "divide")); //Should say 5 in console.
//I hope I helped!