Tuleap front end can be divided in two worlds
Mostly static pages that are rendered server side using mustache templating (with some vanilla JS for simple interactions).
Rich, dynamic, pages that are rendered client side using Vuejs.
Front end build system is based on webpack.
Historically you will also find:
AngularJS 1.X code.
Prototype / Scriptaculous code.
Good old php3&4/mysql scripts where DB, HTML and JS are mixed.
Those are usages and technologies of the past and must be forgotten. New contributions should not be based on them.