Overview

teasel is a parser for JavaScript and TypeScript. You give it text, it gives you a tree.

import { Source, js } from '@teasel/parser';

const { node } = new Source('let answer = 42').parse();

The tree is ESTree: plain objects with a type, a start and an end. Code that walks an ESTree tree walks this one.

Options

Options add to what a parse returns.

const { node, scopes, bindings } = new Source(text, { scopes: true }).parse();

scopes adds what every name declares and what it refers to. Other options add the comments, the errors of a file that does not parse, and a TypeScript file with its types removed. What parse returns lists every option and what it adds.

Parse part of the text

A parse can start at an offset and read one expression, one statement or one pattern.

source.parse(js.expression, 10);

A template language uses this to read the JavaScript inside its own syntax, and to stop at its own tokens: see Embedded JavaScript. A template language can also describe its whole syntax as a grammar, and get a whole file back as one tree: see Parsing with a grammar.

Where it runs

Under Node it is a native addon, and the WebAssembly build where the addon does not load. In a browser, directly or through a bundler, the same import is a WebAssembly build with the same API. Getting started is the first parse. How it works explains what happens during a parse.