Blockly

Blockly is a client-side JavaScript library for building visual programming editors. It provides a block-based interface that allows users to create programs by snapping together draggable blocks instead of typing text. Developed by Google, Blockly is released as open-source software under the Apache License 2.0 and is designed to be embedded into web applications.

Users place blocks in a workspace, where blocks represent programming constructs such as variables, logic, loops, math, and text. The blocks connect through a grid-like snapping mechanism and can be arranged to form syntactically correct programs. Blockly can generate code in multiple languages from the same block arrangement, including JavaScript, Python, PHP, Lua, and Dart. The state of the workspace is typically saved as XML, and blocks can be exported or reloaded.

Block definitions are created in JSON, and developers can define new block types and toolboxes. Blockly supports features such as mutator blocks for dynamic block shapes, variables, procedures (functions), and internationalization. It is designed to be easily integrated into existing web pages and apps and can be themed and extended with custom blocks and generators.

Usage and impact: Blockly has been used in education and web apps to teach programming concepts without text-based syntax. Google maintains Blockly Games, a set of tutorials that teach programming concepts using blocks. The library has been adopted by other projects and educational tools to provide accessible, language-agnostic coding experiences.