esprima

What is esprima?

Esprima is a high performance, standard-compliant ECMAScript parser written in ECMAScript (also popularly known as JavaScript). It is capable of parsing JavaScript code to produce an abstract syntax tree (AST), which can be used for various purposes such as static analysis, code instrumentation, and transformation.

What are esprima's main functionalities?

Parsing JavaScript Code

This feature allows you to parse a string of JavaScript code and obtain an abstract syntax tree (AST) that represents the structure of the code.

const esprima = require('esprima');
const program = 'const answer = 42;';
const ast = esprima.parseScript(program);

Syntax Tree Analysis

Once you have the AST, you can analyze it to extract information about the code, such as variable names, function declarations, and more.

const esprima = require('esprima');
const program = 'const answer = 42;';
const ast = esprima.parseScript(program);
console.log(ast.body[0].declarations[0].id.name); // 'answer'

Tokenization

Esprima can also be used to tokenize JavaScript code, breaking it down into its lexical components (tokens) such as keywords, identifiers, literals, and operators.

const esprima = require('esprima');
const program = 'const answer = 42;';
const tokens = esprima.tokenize(program);
console.log(tokens);

Other packages similar to esprima

acorn

Acorn is a tiny, fast JavaScript parser, also producing an AST. It is similar to Esprima in terms of functionality but focuses on being smaller and more modular.

cherow

Cherow is a very fast, standards-compliant, self-hosted JavaScript parser with error recovery. It compares to Esprima in terms of compliance and performance but also offers better error handling and recovery options.

README

Esprima (esprima.org, BSD license) is a high performance, standard-compliant ECMAScript parser written in ECMAScript (also popularly known as JavaScript). Esprima is created and maintained by Ariya Hidayat, with the help of many contributors.

Features

• Full support for ECMAScript 2016 (ECMA-262 7th Edition)
• Sensible syntax tree format as standardized by ESTree project
• Experimental support for JSX, a syntax extension for React
• Optional tracking of syntax node location (index-based and line-column)
• Heavily tested (~1300 unit tests with full code coverage)

API

Esprima can be used to perform lexical analysis (tokenization) or syntactic analysis (parsing) of a JavaScript programs.

A simple example:

var esprima = require('esprima');
var code = 'const answer = 42';
var tokens = esprima.tokenize(code);
var ast = esprima.parse(code);

which gives a list of tokens:

[ { type: 'Keyword', value: 'const' },
  { type: 'Identifier', value: 'answer' },
  { type: 'Punctuator', value: '=' },
  { type: 'Numeric', value: '42' } ]

and an abstract syntax tree:

{ type: 'Program',
  body:
   [ { type: 'VariableDeclaration',
       declarations: [Object],
       kind: 'const' } ],
  sourceType: 'script' }