tessl/npm-babel-generator

Turns an AST into code.

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Babel Generator

Name: tessl/npm-babel-generator
Author: tessl

Babel Generator converts Abstract Syntax Trees (ASTs) back into JavaScript code with comprehensive formatting options, source map generation, and support for all modern JavaScript features including ES2015+, Flow types, and JSX.

Package Information

Package Name: babel-generator
Package Type: npm
Language: JavaScript
Installation: npm install babel-generator

Core Imports

import generate from "babel-generator";
import { CodeGenerator } from "babel-generator";

For CommonJS:

const generate = require("babel-generator").default;
const { CodeGenerator } = require("babel-generator");

Basic Usage

import generate from "babel-generator";
import * as babylon from "babylon";

// Parse source code into AST
const ast = babylon.parse("const x = 1;");

// Generate code from AST
const output = generate(ast, {
  quotes: "double",
  compact: false
});

console.log(output.code); // "const x = 1;"
console.log(output.map);  // Source map object (if sourceMaps: true)

Architecture

Babel Generator is built around several key components:

Main Generator Function: Single function interface for converting ASTs to code
CodeGenerator Class: Class-based interface providing the same functionality
Printer Class: Core printing engine handling code generation and formatting
AST Node Generators: Specialized methods for each AST node type (expressions, statements, types, etc.)
Output Formatting: Comprehensive options for whitespace, quotes, minification, and source maps
Source Map Support: Optional source map generation with multi-file support

Capabilities

Code Generation

Main API for converting ASTs into JavaScript code with customizable formatting options.

function generate(
  ast: Object,
  opts?: GeneratorOptions,
  code?: string | Object
): GeneratorResult;

class CodeGenerator {
  constructor(ast: Object, opts?: GeneratorOptions, code?: string | Object);
  generate(): GeneratorResult;
}

interface GeneratorResult {
  code: string;
  map?: Object;
  rawMappings?: Array<{
    generated: { line: number; column: number };
    original: { line: number; column: number };
    source: string;
    name?: string;
  }>;
}

Code Generation

Formatting Options

Extensive configuration for output style including whitespace control, quote preferences, and minification.

interface GeneratorOptions {
  auxiliaryCommentBefore?: string;
  auxiliaryCommentAfter?: string;
  shouldPrintComment?: (comment: string) => boolean;
  retainLines?: boolean;
  retainFunctionParens?: boolean;
  comments?: boolean;
  compact?: boolean | "auto";
  minified?: boolean;
  concise?: boolean;
  quotes?: "single" | "double";
  filename?: string;
  flowCommaSeparator?: boolean;
  jsonCompatibleStrings?: boolean;
}

Formatting Options

Source Map Generation

Optional source map support for debugging and development tools integration.

interface SourceMapOptions {
  sourceMaps?: boolean;
  sourceMapTarget?: string;
  sourceRoot?: string;
  sourceFileName?: string;
}

Source Maps

AST Node Support

Comprehensive support for all JavaScript, Flow, and JSX AST node types with specialized generation methods.

// Core node types supported:
// - Base nodes (File, Program, BlockStatement, etc.)
// - Expression nodes (CallExpression, BinaryExpression, etc.)
// - Statement nodes (IfStatement, ForStatement, etc.)
// - Type & literal nodes (Identifier, StringLiteral, etc.)
// - Class nodes (ClassDeclaration, ClassMethod, etc.)
// - Method nodes (FunctionExpression, ArrowFunctionExpression, etc.)
// - Module nodes (ImportDeclaration, ExportDeclaration, etc.)
// - Flow type nodes (TypeAnnotation, InterfaceDeclaration, etc.)
// - JSX nodes (JSXElement, JSXAttribute, etc.)
// - Template literal nodes (TemplateLiteral, etc.)

AST Node Support

Advanced Features

Advanced functionality including multi-source handling, custom formatting, and integration utilities.

// Multi-source usage
const sources = {
  'file1.js': 'source code 1',
  'file2.js': 'source code 2'
};
const result = generate(combinedAst, { sourceMaps: true }, sources);

// Helper utilities for whitespace and parentheses detection
function needsWhitespace(node: Object, parent: Object, type: string): number;
function needsParens(node: Object, parent: Object, printStack: Array): boolean;

Advanced Features