Answer by royse41 for Bootstrap 3 collapse change chevron icon on click

The problem is with your jQuery code not being correct.

You're closing the event handler function early on this line:

$('#serviceList').on('shown.bs.collapse'), function() {

See that second closing parenthesis? That's closing the 'on' function early. Try changing your jQuery to look like this:

$('#serviceList').on('shown.bs.collapse', function() {    $(".servicedrop").addClass('glyphicon-chevron-up').removeClass('glyphicon-chevron-down');  });$('#serviceList').on('hidden.bs.collapse', function() {    $(".servicedrop").addClass('glyphicon-chevron-down').removeClass('glyphicon-chevron-up');  });