on click add class in jquery code example

Example 1: jquery on click add class

$(document).ready(function(){
  $("button").click(function(){
    $(".p").addClass("intro");
  });
});

Example 2: javascript add class to element

var someElement= document.getElementById("myElement");
    someElement.className += " newclass";//add "newclass" to element (space in front is important)