Make a SharePoint List form field read only with jQuery

Steps
 
Edit your SharePoint page and add a script editor.
 
Paste the below code in your script editor.
 
Source code
  1. <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.1/jquery.min.js"    
  2.        type="text/javascript"></script>    
  3.      
  4. <script type="text/javascript">    
  5.      
  6. $(document).ready(function()    
  7. {    
  8. //Set the Field to Read only and change its background colour    
  9. $("input[title='FieldName']").attr("readonly","true").css('background-color','#F6F6F6');    
  10.     
  11. });