index.js

function getGrade(theo, pract, project) {
  //Test if theo, prac, project is 0:

  theo = +document.getElementById('theo').value;
  pract = +document.getElementById('pract').value;
  project = +document.getElementById('project').value;

  return ((theo === 5 || pract === 5 || project === 5) ? 'Du musst wohl nochmal ran 😓' :
    (theo === 0 || pract === 0 || project === 0) ? 'Du hast noch nicht alles abgegeben 😓' :
      (theo * 2 + pract + project) / 4);
}
function displayResult() {
  document.getElementById('result').innerHTML = getGrade(theo, pract, project);
}

document.getElementById('calculate').addEventListener('click', displayResult);
document.getElementById('calculate').addEventListener('click', celebrations);

// // Display celebrations gif if the value of #result is between 1.0 and 2.3:

// function celebrations(result) {
//   return (document.getElementById('result').innerHTML <= 3) ? console.log("good") : console.log("bad");
// }

// function showGif() {

// }