Babel compiler core.
Last updated 4 years ago by everthis .
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Babel compiler core.

var babel = require("babel-core");
import { transform } from 'babel-core';
import * as babel from 'babel-core';

babel.transform(code: string, options?: Object)

Transforms the passed in code. Returning an object with the generated code, source map, and AST.

babel.transform(code, options) // => { code, map, ast }


var result = babel.transform("code();", options);

babel.transformFile(filename: string, options?: Object, callback: Function)

Asynchronously transforms the entire contents of a file.

babel.transformFile(filename, options, callback)


babel.transformFile("filename.js", options, function (err, result) {
  result; // => { code, map, ast }

babel.transformFileSync(filename: string, options?: Object)

Synchronous version of babel.transformFile. Returns the transformed contents of the filename.

babel.transformFileSync(filename, options) // => { code, map, ast }


babel.transformFileSync("filename.js", options).code;

babel.transformFromAst(ast: Object, code?: string, options?: Object)

Given, an AST, transform it.

const code = "if (true) return;";
const ast = babylon.parse(code, { allowReturnOutsideFunction: true });
const { code, map, ast } = babel.transformFromAst(ast, code, options);


Babel CLI

You can pass these options from the Babel CLI like so:

babel --name=value

Following is a table of the options you can use:

Option Default Description
filename "unknown" Filename for use in errors etc.
filenameRelative (filename) Filename relative to sourceRoot.
presets [] List of presets (a set of plugins) to load and use.
plugins [] List of plugins to load and use.
parserOpts {} An object containing the options to be passed down to the babel parser, babylon
generatorOpts {} An object containing the options to be passed down to the babel code generator, babel-generator
highlightCode true ANSI highlight syntax error code frames
only null A glob, regex, or mixed array of both, matching paths to only compile. Can also be an array of arrays containing paths to explicitly match. When attempting to compile a non-matching file it's returned verbatim.
ignore null Opposite to the only option. ignore is disregarded if only is specified.
auxiliaryCommentBefore null Attach a comment before all non-user injected code.
auxiliaryCommentAfter null Attach a comment after all non-user injected code.
sourceMaps false If truthy, adds a map property to returned output. If set to "inline", a comment with a sourceMappingURL directive is added to the bottom of the returned code. If set to "both" then a map property is returned as well as a source map comment appended. This does not emit sourcemap files by itself! To have sourcemaps emitted using the CLI, you must pass it the --source-maps option.
inputSourceMap null A source map object that the output source map will be based on.
sourceMapTarget (filenameRelative) Set file on returned source map.
sourceFileName (filenameRelative) Set sources[0] on returned source map.
sourceRoot (moduleRoot) The root from which all sources are relative.
moduleRoot (sourceRoot) Optional prefix for the AMD module formatter that will be prepend to the filename on module definitions.
moduleIds false If truthy, insert an explicit id for modules. By default, all modules are anonymous. (Not available for common modules)
moduleId null Specify a custom name for module ids.
getModuleId null Specify a custom callback to generate a module id with. Called as getModuleId(moduleName). If falsy value is returned then the generated module id is used.
resolveModuleSource null Resolve a module source ie. import "SOURCE"; to a custom value. Called as resolveModuleSource(source, filename).
code true Enable code generation
no-babelrc CLI flag Specify whether or not to use .babelrc and .babelignore files. Only available when using the CLI.
ast true Include the AST in the returned object
compact "auto" Do not include superfluous whitespace characters and line terminators. When set to "auto" compact is set to true on input sizes of >500KB.
minified false Should the output be minified (not printing last semicolons in blocks, printing literal string values instead of escaped ones, stripping () from new when safe)
comments true Output comments in generated output.
shouldPrintComment null An optional callback that controls whether a comment should be output or not. Called as shouldPrintComment(commentContents). NOTE: This overrides the comment option when used.
env {} This is an object of keys that represent different environments. For example, you may have: { env: { production: { /* specific options */ } } } which will use those options when the enviroment variable BABEL_ENV is set to "production". If BABEL_ENV isn't set then NODE_ENV will be used, if it's not set then it defaults to "development"
retainLines false Retain line numbers. This will lead to wacky code but is handy for scenarios where you can't use source maps. (NOTE: This will not retain the columns)
extends null A path to an .babelrc file to extend

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