Turns an AST into code.

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6.26.15 years ago8 years agoMinified + gzip package size for babel-generator in KB


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.