input field focus in javascript code example

Example 1: set focus javascript

document.getElementById("ThingToSetFocusOn").focus();

Example 2: 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 3: focus js

focusMethod = function getFocus() {           
  document.getElementById("myTextField").focus();
}