input on focus in code example

Example 1: html prevent focus on input

<input type="text" id="yourID" value="test" readonly="readonly" /> 

You can change it in javascript with : 

document.getElementById("yourID").readOnly = false; //This enables the possibility to focus

Example 2: js focus event

const form = document.getElementById('form');

form.addEventListener('focus', (event) => {
  event.target.style.background = 'pink';    
}, true);

form.addEventListener('blur', (event) => {
  event.target.style.background = '';    
}, true);