Javascript checkbox onChange

Question

I have a checkbox in a form and I\'d like it to work according to following scenario:

• if someone checks it, the value of a textfield (totalCost)

Answer 1

Pure javascript:

const checkbox = document.getElementById('myCheckbox')

checkbox.addEventListener('change', (event) => {
  if (event.target.checked) {
    alert('checked');
  } else {
    alert('not checked');
  }
})

My Checkbox: