Install

  1. npm install --save-dev @babel/generator

Usage

  1. import {parse} from '@babel/parser';
  2. import generate from '@babel/generator';
  3. const code = 'class Example {}';
  4. const ast = parse(code);
  5. const output = generate(ast, { /* options */ }, code);

Options

Options for formatting output:

nametypedefaultdescription
auxiliaryCommentBeforestringOptional string to add as a block comment at the start of the output file
auxiliaryCommentAfterstringOptional string to add as a block comment at the end of the output file
shouldPrintCommentfunctionopts.commentsFunction 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.minified is false and the comment contains @preserve or @license
retainLinesbooleanfalseAttempt to use the same line numbers in the output code as in the source code (helps preserve stack traces)
retainFunctionParensbooleanfalseRetain parens around function expressions (could be used to change engine parsing behavior)
commentsbooleantrueShould comments be included in output
compactboolean or 'auto'opts.minifiedSet to true to avoid adding whitespace for formatting
minifiedbooleanfalseShould the output be minified
concisebooleanfalseSet to true to reduce whitespace (but not as much as opts.compact)
filenamestringUsed in warning messages
jsonCompatibleStringsbooleanfalseSet to true to run jsesc with "json": true to print "\u00A9" vs. "©";

Options for source maps:

nametypedefaultdescription
sourceMapsbooleanfalseEnable generating source maps
sourceRootstringA root for all relative URLs in the source map
sourceFileNamestringThe 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 needto pass an object to generate as the code parameter. Keysshould be the source filenames, and values should be the source content.

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

  1. import {parse} from '@babel/parser';
  2. import generate from '@babel/generator';
  3. const a = 'var a = 1;';
  4. const b = 'var b = 2;';
  5. const astA = parse(a, { sourceFilename: 'a.js' });
  6. const astB = parse(b, { sourceFilename: 'b.js' });
  7. const ast = {
  8. type: 'Program',
  9. body: [].concat(astA.program.body, astB.program.body)
  10. };
  11. const { code, map } = generate(ast, { sourceMaps: true }, {
  12. 'a.js': a,
  13. 'b.js': b
  14. });
  15. // Sourcemap will point to both a.js and b.js where appropriate.