autosizejs

Autosize.js is a lightweight, dependency-free JavaScript library that automatically adjusts the height of textarea elements to fit their content as users type. By resizing instead of introducing scrollbars, it helps maintain a clean layout in forms and comment fields.

The script attaches to textarea elements and recalculates height on input or change events. The common approach is to temporarily set the element’s height to auto, read the scrollHeight, and then apply that value as the new height. This allows the control to expand as content grows, while staying compact when empty. It can handle multiple textareas on a page and responds to window resizes and programmatic updates.

Features and options typically include automatic resizing on content changes, support for multiple textareas, and the ability to constrain minimum and maximum heights. It also provides a destroy mechanism to remove all event listeners when the feature is no longer needed.

Usage is straightforward: include the autosize script in a page and invoke the API on the desired textareas, for example autosize(document.querySelectorAll('textarea')). It is designed for use without jQuery and works in modern browsers.

History and ecosystem: Autosize.js has seen broad adoption and has multiple contributors, with various forks and integrations in web projects. It remains a compact solution for dynamic text input without requiring heavy UI libraries.