gulpjs/gulp

Gulp is a build automation toolkit for JavaScript projects. The problem it solves is that front-end development involves many repetitive file-processing tasks: compiling LESS or SASS stylesheets into plain CSS, transpiling modern JavaScript into older browser-compatible versions, minifying files to reduce their size, combining multiple files into one, renaming files, and so on. Doing these steps manually every time you change a file is tedious and error-prone. Gulp lets you define these tasks once in code and run them with a single command. The way it works is through a concept called streams and pipes. You point Gulp at a set of source files using a glob pattern (like "all .less files in the styles folder"), then chain a series of transformations using .pipe(), much like an assembly line where each station does one thing to the file before passing it along. At the end of the chain, you write the result to a destination folder. Tasks can run one after another or in parallel, and a watch mode will automatically re-run relevant tasks whenever you save a file during development. Gulp's API is small by design: you mainly use src (to pick files), dest (to write them), pipe (to apply transformations), series (run tasks sequentially), parallel (run tasks simultaneously), and watch (react to file changes). The actual transformations are handled by plugins from the npm ecosystem, there are thousands covering image optimization, HTML templating, TypeScript compilation, linting, testing, and more. Developers reach for Gulp when they need a flexible, code-based build pipeline for a web project. It runs on Node.js, integrates with all major code editors, and works alongside any server-side language. The gulpfile is just a regular JavaScript or ES module file, so the full power of Node.js is available for custom logic.