jquery addClass() not working with event.target

    e.currentTarget.classList.add("loading_arrow");

you can use above line to add loading_arrow class using js mouse event.

You have two problem:

$(this).addClass("big"); //Unquote to "this"
$(e.target).addClass("big"); // select e.target with $() wrapper.

Basically e.target will be a javascript object, you have to convert it into a Jquery object before utilizing its functions like .addClass()

Try,

$(e.target).addClass("big"); 

and at the same time, $("this").addClass("big"); this code will not work since you are passing this as a string. this also a javascript object, you need to convert that too as a jquery object like $(this)