Gulp is an open source JavaScript-based task runner, which uses code-over-configuration approach to define its tasks. These could be the following:

• Bundling and minifying libraries and style sheets
• Refreshing your browser when you save a file
• Quickly running unit tests
• Running code analysis
• LESS/SASS to CSS compilation
• Copying modified files to an output directory

This tool uses the stream module of Node.js; first of all, we need to define what a stream is. It can be defined as a tool that allows data reading on one file and takes it to another place through pipes methods. The principal feature of Gulp.js is that it does not write files/folders into the hard drive, like other automation tools. That's a good feature, because we can configure several tasks, and it won't impact our computer performance.