Is it possible to focus on a using JavaScript focus() function?

Answer 1

Yes - this is possible. In order to do it, you need to assign a tabindex...

Hello World

A tabindex of 0 will put the tag "in the natural tab order of the page". A higher number will give it a specific order of priority, where 1 will be the first, 2 second and so on.

You can also give a tabindex of -1, which will make the div only focus-able by script, not the user.

document.getElementById('test').onclick = function () {
    document.getElementById('scripted').focus();
};

div:focus {
    background-color: Aqua;
}

Element X (not focusable)
Element Y (user or script focusable)
Element Z (script-only focusable)
Set Focus To Element Z

Obviously, it is a shame to have an element you can focus by script that you can't focus by other input method (especially if a user is keyboard only or similarly constrained). There are also a whole bunch of standard elements that are focusable by default and have semantic information baked in to assist users. Use this knowledge wisely.