RJs

RJS, short for Ruby JavaScript, is a historical term associated with the Ruby on Rails web framework for generating JavaScript responses on the server in response to Ajax requests. In this approach, developers wrote templates with the .rjs extension containing Ruby code that, when evaluated on the server, produced JavaScript sent to the browser. The output JavaScript would typically modify the page DOM—updating content, inserting or removing elements, or triggering visual effects—without requiring a full page reload.

RJS templates often relied on a page object to issue commands that translated into client-side actions, such as replacing HTML content or applying effects. The templates could call methods like page.replace_html or page.visual_effect to describe the desired updates. This tightly couples server-side logic with client-side behavior, as the server dictates the exact JavaScript to execute in the browser.

The use of RJS was most common during the early Rails era, roughly from the mid-2000s through the late 2000s. As web development practices evolved toward unobtrusive JavaScript and front-end frameworks, RJS declined in popularity. Modern Rails development typically uses alternatives such as .js.erb templates, Rails UJS, or front-end technologies that separate concerns between server responses and client-side logic.

See also: Ruby on Rails, AJAX, JavaScript, .js.erb, Rails UJS.