There is a simple form which takes two numbers num1, num2 and an operation op. After submission, a new object is created. I'm new to OOJS and any correction and improvements are appreciated. Is this the best way to code this small calculator in Javascript using Object Oriented approach?

window.onload = function() {

  let form = document.forms['cal-form'];
  form.addEventListener('submit', calculate);

  function calculate(e) {
    //prevent default form submission
    e.preventDefault();
    //get form values`enter code here`
    let num1 = parseInt(document.getElementsByTagName('input')[0].value);
    let num2 = parseInt(document.getElementsByTagName('input')[1].value);
    let op = document.getElementsByTagName('select')[0].value;

    //create object constructor function
    function Calculate(num1, num2, op){
      this.num1 = num1;
      this.num2 = num2;
      this.op = op;
    } 

    Calculate.prototype.result = function() {
      let res;
      switch (op) {
        case 'add':
          res = this.num1 + this.num2;
          break;
        case 'sub':
          res = this.num1 - this.num2;
          break;
        case 'mul':
          res = this.num1 * this.num2;
          break;
        case 'div':
          res = this.num1 / this.num2;
          break;
        default:
          res= 'Error! No operation selected.';
      }
      return res;
    };

    //create an object
    let cal = new Calculate(num1, num2, op);
    //display result
    document.getElementById('result').innerHTML = cal.result();

  }
};

There is a simple form which takes two numbers num1, num2 and an operation op. After submission, a new object is created. I'm new to OOJS and any correction and improvements are appreciated. Is this the best way to code this small calculator in Javascript using Object Oriented approach?

window.onload = function() {

  let form = document.forms['cal-form'];
  form.addEventListener('submit', calculate);

  function calculate(e) {
    //prevent default form submission
    e.preventDefault();
    //get form values
    let num1 = parseInt(document.getElementsByTagName('input')[0].value);
    let num2 = parseInt(document.getElementsByTagName('input')[1].value);
    let op = document.getElementsByTagName('select')[0].value;

    //create object constructor function
    function Calculate(num1, num2, op){
      this.num1 = num1;
      this.num2 = num2;
      this.op = op;
    } 

    Calculate.prototype.result = function() {
      let res;
      switch (op) {
        case 'add':
          res = this.num1 + this.num2;
          break;
        case 'sub':
          res = this.num1 - this.num2;
          break;
        case 'mul':
          res = this.num1 * this.num2;
          break;
        case 'div':
          res = this.num1 / this.num2;
          break;
        default:
          res= 'Error! No operation selected.';
      }
      return res;
    };

    //create an object
    let cal = new Calculate(num1, num2, op);
    //display result
    document.getElementById('result').innerHTML = cal.result();

  }
};

There is a simple form which takes two numbers num1, num2 and operation (op). After submission, a new object is created. I'm new to OOJS and any correction and improvements are appreciated.

window.onload = function() {

  let form = document.forms['cal-form'];
  form.addEventListener('submit', calculate);

  function calculate(e) {
    //prevent default form submission
    e.preventDefault();
    //get form values`enter code here`
    let num1 = parseInt(document.getElementsByTagName('input')[0].value);
    let num2 = parseInt(document.getElementsByTagName('input')[1].value);
    let op = document.getElementsByTagName('select')[0].value;

    //create object constructor function
    function Calculate(num1, num2, op){
      this.num1 = num1;
      this.num2 = num2;
      this.op = op;
    } 

    Calculate.prototype.result = function() {
      let res;
      switch (op) {
        case 'add':
          res = this.num1 + this.num2;
          break;
        case 'sub':
          res = this.num1 - this.num2;
          break;
        case 'mul':
          res = this.num1 * this.num2;
          break;
        case 'div':
          res = this.num1 / this.num2;
          break;
        default:
          res= 'Error! No operation selected.';
      }
      return res;
    };

    //create an object
    let cal = new Calculate(num1, num2, op);
    //display result
    document.getElementById('result').innerHTML = cal.result();

  }
};

There is a simple form which takes two numbers num1, num2 and an operation op. After submission, a new object is created. I'm new to OOJS and any correction and improvements are appreciated. Is this the best way to code this small calculator in Javascript using Object Oriented approach?

window.onload = function() {

  let form = document.forms['cal-form'];
  form.addEventListener('submit', calculate);

  function calculate(e) {
    //prevent default form submission
    e.preventDefault();
    //get form values`enter code here`
    let num1 = parseInt(document.getElementsByTagName('input')[0].value);
    let num2 = parseInt(document.getElementsByTagName('input')[1].value);
    let op = document.getElementsByTagName('select')[0].value;

    //create object constructor function
    function Calculate(num1, num2, op){
      this.num1 = num1;
      this.num2 = num2;
      this.op = op;
    } 

    Calculate.prototype.result = function() {
      let res;
      switch (op) {
        case 'add':
          res = this.num1 + this.num2;
          break;
        case 'sub':
          res = this.num1 - this.num2;
          break;
        case 'mul':
          res = this.num1 * this.num2;
          break;
        case 'div':
          res = this.num1 / this.num2;
          break;
        default:
          res= 'Error! No operation selected.';
      }
      return res;
    };

    //create an object
    let cal = new Calculate(num1, num2, op);
    //display result
    document.getElementById('result').innerHTML = cal.result();

  }
};