Upupdown

Upupdown is a term used in web development and video game design to describe a simple pattern-based keyboard input system. In its most common form it refers to lightweight libraries or utilities that detect a sequence of key presses—often arrow keys and certain letters—and trigger actions when the sequence matches a preconfigured pattern. The name evokes the idea of pressing Up, Up, Down, Down, a nod to the broader family of Easter-egg sequences popular on the web and in games.

Design and features: A typical upupdown utility listens for keydown events, normalizes key codes to a small set of commands (up, down, left, right, a, b), and maintains a progress pointer for each configured sequence. It supports customization of the required sequence, a time limit to reset progress, and a callback that fires when the sequence completes. Some implementations support multiple sequences, optional overlaps, and suppression of default browser behavior.

Usage: Developers use upupdown to embed Easter eggs or hidden features in websites or games. Common examples include unlocking a debug console, revealing hidden themes, or triggering celebratory animations.

History and reception: The concept grew from the broader practice of keyboard Easter eggs and the Konami code. Multiple independent libraries and snippets exist, leading to a small ecosystem of lightweight, dependency-free utilities.

See also: Konami code, keyboard shortcut, Easter egg.