Link to a PDF taking about which JS Frameworks help against JS hijacking and how JS hijacking works
Javascript Tools provides a common set of methods extending those available in Drupal core (drupal.js) for Javascript and AJAX module development in Drupal.
jQuery is a Javascript library that takes this motto to heart: Writing Javascript code should be fun. jQuery acheives this goal by taking common, repetitive, tasks, stripping out all the unnecessary markup, and leaving them short, smart and understandable
Prototype is a JavaScript framework that aims to ease development of dynamic web applications.