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Turns an AST into code.


npm install --save-dev babel-generator


import {parse} from 'babylon';
import generate from 'babel-generator';
const code = 'class Example {}';
const ast = parse(code);
const output = generate(ast, { /* options */ }, code);


Options for formatting output:

name type default description
auxiliaryCommentBefore string Optional string to add as a block comment at the start of the output file
auxiliaryCommentAfter string Optional string to add as a block comment at the end of the output file
shouldPrintComment function opts.comments Function that takes a comment (as a string) and returns true if the comment should be included in the output. By default, comments are included if opts.comments is true or if opts.minifed is false and the comment contains @preserve or @license
retainLines boolean false Attempt to use the same line numbers in the output code as in the source code (helps preserve stack traces)
retainFunctionParens boolean false Retain parens around function expressions (could be used to change engine parsing behavior)
comments boolean true Should comments be included in output
compact boolean or 'auto' opts.minified Set to true to avoid adding whitespace for formatting
minified boolean false Should the output be minified
concise boolean false Set to true to reduce whitespace (but not as much as opts.compact)
quotes 'single' or 'double' autodetect based on ast.tokens The type of quote to use in the output
filename string Used in warning messages
flowCommaSeparator boolean false Set to true to use commas instead of semicolons as Flow property separators
jsonCompatibleStrings boolean false Set to true to run jsesc with "json": true to print "\u00A9" vs. "©";

Options for source maps:

name type default description
sourceMaps boolean false Enable generating source maps
sourceMapTarget string The filename of the generated code that the source map will be associated with
sourceRoot string A root for all relative URLs in the source map
sourceFileName string The filename for the source code (i.e. the code in the code argument). This will only be used if code is a string.

AST from Multiple Sources

In most cases, Babel does a 1:1 transformation of input-file to output-file. However, you may be dealing with AST constructed from multiple sources - JS files, templates, etc. If this is the case, and you want the sourcemaps to reflect the correct sources, you'll need to pass an object to generate as the code parameter. Keys should be the source filenames, and values should be the source content.

Here's an example of what that might look like:

import {parse} from 'babylon';
import generate from 'babel-generator';
const a = 'var a = 1;';
const b = 'var b = 2;';
const astA = parse(a, { sourceFilename: 'a.js' });
const astB = parse(b, { sourceFilename: 'b.js' });
const ast = {
  type: 'Program',
  body: [].concat(astA.program.body, astB.program.body)
const { code, map } = generate(ast, { sourceMaps: true }, {
  'a.js': a,
  'b.js': b
// Sourcemap will point to both a.js and b.js where appropriate.