esprima

Esprima is a JavaScript parser: a tool that reads JavaScript code and breaks it down into a structured representation that other programs can analyze. When you write JavaScript, it is just text. A parser turns that text into a tree of objects that describes the code's structure, showing which parts are variable declarations, which are function calls, which are loops, and so on. This tree format is called an abstract syntax tree.

Developers use parsers like Esprima as a building block for tools that work with code programmatically. Linters that check code for style or errors, formatters that reformat code automatically, bundlers that combine files, and code analysis tools all typically rely on parsing JavaScript first. Esprima provides that foundation.

The library supports JavaScript up to the ECMAScript 2019 standard, which is the version of JavaScript formalized that year. It also has experimental support for JSX, a syntax extension used in React applications that lets developers write HTML-like markup inside JavaScript. The output tree follows a standardized format maintained by the ESTree project, which means Esprima's output is compatible with many other tools that expect that format.

Esprima is available as an npm package, so it can be installed with a standard JavaScript package manager and used in Node.js projects. It is maintained under the jQuery organization on GitHub and released under the BSD license, which permits free use in commercial and open-source projects. The README is brief; fuller documentation is available on the project's website.