Documentation

Complete guide to using the Esprima parser

Try the parser • Learn about Esprima • View examples

Installation

Install Esprima using npm or yarn:

npm install esprima

yarn add esprima

Basic Usage

Import and use Esprima to parse JavaScript code:

import * as esprima from 'esprima';

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

console.log(JSON.stringify(ast, null, 2));

This will output the Abstract Syntax Tree representation of your JavaScript code.

API Reference

parseScript(code, options?)

Parses JavaScript code as a script (not a module).

Parameters:

code (string): The JavaScript code to parse
options (object, optional): Parser configuration options

Returns:

An AST object representing the parsed code

parseModule(code, options?)

Parses JavaScript code as an ES6 module.

Parameters:

code (string): The JavaScript module code to parse
options (object, optional): Parser configuration options

Returns:

An AST object representing the parsed module

tokenize(code, options?)

Tokenizes JavaScript code without building the full AST.

Parameters:

code (string): The JavaScript code to tokenize
options (object, optional): Tokenizer options

Returns:

An array of token objects

Parser Options

Customize the parser behavior with these options:

range

Type: boolean

Default: false

Include start and end positions for each node

loc

Type: boolean

Default: false

Include line and column location for each node

tokens

Type: boolean

Default: false

Collect tokens in the output

comment

Type: boolean

Default: false

Collect comments in the output

jsx

Type: boolean

Default: false

Enable JSX syntax support

tolerant

Type: boolean

Default: false

Continue parsing after errors

Example with Options

const ast = esprima.parseScript(code, {
  range: true,
  loc: true,
  tokens: true,
  comment: true
});

Understanding AST

The Abstract Syntax Tree (AST) is a tree representation of your code's structure. Each node in the tree represents a construct in your code.

Common Node Types

Program

The root node of every AST, containing all top-level statements

VariableDeclaration

Variable declarations (const, let, var)

FunctionDeclaration

Function declarations and expressions

CallExpression

Function and method calls

BinaryExpression

Binary operations like +, -, *, /

Identifier

Variable and function names

Example AST Structure

// Code: const x = 5;

{
  "type": "Program",
  "body": [{
    "type": "VariableDeclaration",
    "declarations": [{
      "type": "VariableDeclarator",
      "id": {
        "type": "Identifier",
        "name": "x"
      },
      "init": {
        "type": "Literal",
        "value": 5
      }
    }],
    "kind": "const"
  }]
}

Error Handling

Esprima throws errors when it encounters invalid JavaScript syntax. Always wrap parsing in try-catch blocks:

try {
  const ast = esprima.parseScript(code);
  // Process the AST
} catch (error) {
  console.error('Parse error:', error.message);
  // Error includes line, column, and description
}

Error Properties

message: Human-readable error description
lineNumber: Line where the error occurred
column: Column where the error occurred
description: Detailed error information

Additional Resources

Official Esprima Website

Visit the official documentation and resources

GitHub Repository

View source code and contribute to the project

Code Examples

See practical examples of Esprima in action