script.js

// get required elements
const inputAngels = document.getElementsByClassName("input-angle");
const btnCheck = document.getElementById("btn-check");
const divOutput = document.getElementById("div-output");

// addEventListener for check btn click
btnCheck.addEventListener("click", () => {
  // get sum of elements
  let sum = getSum();
  if (sum !== undefined) inform(sum);
});

// arrow function to calculate sum.
const getSum = () => {
  let sum = 0;
  for (let i = 0; i < 3; i++) {
    if (inputAngels[i].value === "" || Number(inputAngels[i].value) < 0) {
      inform();
      return undefined;
    } else {
      sum += Number(inputAngels[i].value);
    }
  }
  return sum;
};

// arrow function to set the message (result)
const inform = (sum = "") => {
  let message;
  if (sum === "") message = "Enter positive numbers for each angle.";
  else if (sum === 180)
    message = "<strong>Yes!</strong> given angel can form a triangle.🎉️";
  else message = "<strong>No!</strong> given angel can NOT form a triangle.";
  divOutput.innerHTML = message;
  divOutput.className = divOutput.className+ " border-norm round-hf";
};