Getting and changing the contents of javascript form fields

Something like this:

1. document.getElementById('calc').result.value = a;
2. document.getElementById('calc').choice.addEventListener('change', function(e) { if (1 == this.value) doMyFunction(); });
3. var b = document.getElementById('calc').num.value;

I will explain:

1. document.getElementById(id) - getting the element with the specified id ;
2. Historically, <form> elements have a magical property. It allows you to access form input fields directly by the name of the field itself, as properties of this object (in fact, there is an appeal to the elements collection);
3. Each <input> element has a value property that contains the current value of this element.