@babel/core

@babel/core

Babel compiler core.

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

All transformations will use your local configuration files (.babelrc or in package.json). See options to disable it.

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

Transforms the passed in code. Calling a callback with an object with the generated code, source map, and AST.

babel.transform(code, options, function(err, result) {
  result; // => { code, map, ast }
});

Example

babel.transform("code();", options, function(err, result) {
  result.code;
  result.map;
  result.ast;
});

Compat Note:

In Babel 6, this method was synchronous and transformSync did not exist. For backward-compatibility, this function will behave synchronously if no callback is given. If you're starting with Babel 7 and need synchronous behavior, please use transformSync since this backward-compat may be dropped in future major versions of Babel.

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

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

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

Example

var result = babel.transformSync("code();", options);
result.code;
result.map;
result.ast;

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

Asynchronously transforms the entire contents of a file.

babel.transformFile(filename, options, callback)

Example

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 }

Example

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

babel.transformFromAst(ast: Object, code?: string, options?: Object, callback: Function): FileNode | null

Given an AST, transform it.

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

Compat Note:

In Babel 6, this method was synchronous and transformFromAstSync did not exist. For backward-compatibility, this function will behave synchronously if no callback is given. If you're starting with Babel 7 and need synchronous behavior, please use transformFromAstSync since this backward-compat may be dropped in future major versions of Babel.

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

Given an AST, transform it.

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

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

Given some code, parse it using Babel's standard behavior. Referenced presets and plugins will be loaded such that optional syntax plugins are automatically enabled.

Advanced APIs

Many systems that wrap Babel like to automatically inject plugins and presets, or override options. To accomplish this goal, Babel exposes several functions that aid in loading the configuration part-way without transforming.

babel.loadOptions(options?: Object)

Resolve Babel's options fully, resulting in an options object where:

• opts.plugins is a full list of Plugin instances.
• opts.presets is empty and all presets are flattened into opts.
• It can be safely passed back to Babel. Fields like babelrc have been set to false so that later calls to Babel will not make a second attempt to load config files.

Plugin instances aren't meant to be manipulated directly, but often callers will serialize this opts to JSON to use it as a cache key representing the options Babel has received. Caching on this isn't 100% guaranteed to invalidate properly, but it is the best we have at the moment.

babel.loadPartialConfig(options?: Object): PartialConfig

To allow systems to easily manipulate and validate a user's config, this function resolves the plugins and presets and proceeds no further. The expectation is that callers will take the config's .options, manipulate it as then see fit and pass it back to Babel again.

• babelrc: string | void - The path of the .babelrc file, if there was one.
• babelignore: string | void - The path of the .babelignore file, if there was one.
• options: ValidatedOptions - The partially resolved options, which can be manipulated and passed back to Babel again.
  • plugins: Array<ConfigItem> - See below.
  • presets: Array<ConfigItem> - See below.
  • It can be safely passed back to Babel. Fields like babelrc have been set to false so that later calls to Babel will not make a second attempt to load config files.
• hasFilesystemConfig(): boolean - Check if the resolved config loaded any settings from the filesystem.

ConfigItem instances expose properties to introspect the values, but each item should be treated as immutable. If changes are desired, the item should be removed from the list and replaced with either a normal Babel config value, or with a replacement item created by babel.createConfigItem. See that function for information about ConfigItem fields.

babel.createConfigItem(value: string | {} | Function | [string | {} | Function, {} | void], { dirname?: string, type?: "preset" | "plugin" }): ConfigItem

Allows build tooling to create and cache config items up front. If this function is called multiple times for a given plugin, Babel will call the plugin's function itself multiple times. If you have a clear set of expected plugins and presets to inject, pre-constructing the config items would be recommended.

ConfigItem type

Each ConfigItem exposes all of the information Babel knows. The fields are:

• value: {} | Function - The resolved value of the plugin.
• options: {} | void - The options object passed to the plugin.
• dirname: string - The path that the options are relative to.
• name: string | void - The name that the user gave the plugin instance, e.g. plugins: [ ['env', {}, 'my-env'] ]
• file: Object | void - Information about the plugin's file, if Babel knows it.
  • request: string - The file that the user requested, e.g. "@babel/env"
  • resolved: string - The full path of the resolved file, e.g. "/tmp/node_modules/@babel/preset-env/lib/index.js"

Options

Babel CLI

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

babel --option-name=value

Following is a table of the options you can use:

Option	Default	Description
ast	false	Include the AST in the returned object
auxiliaryCommentAfter	null	Attach a comment after all non-user injected code
auxiliaryCommentBefore	null	Attach a comment before all non-user injected code
root	"."	Specify the "root" folder that defines the location to search for "babel.config.js", and the default folder to allow .babelrc files inside of.
configFile	undefined	The config file to load Babel's config from. Defaults to searching for "babel.config.js" inside the "root" folder. false will disable searching for config files.
babelrc	true	Specify whether or not to use .babelrc and .babelignore files. Not available when using the CLI, use --no-babelrc instead
babelrcRoots	(root)	Specify which packages should be search for .babelrc files when they are being compiled. true to always search, or a path string or an array of paths to packages to search inside of. Defaults to only searching the "root" package.
envName	env vars	Defaults to environment variable BABEL_ENV if set, or else NODE_ENV if set, or else it defaults to "development"
code	true	Enable code generation
comments	true	Output comments in generated output
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
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 envName is production
extends	null	A path to a .babelrc file to extend
filename	"unknown"	Filename for use in errors etc
filenameRelative	(filename)	Filename relative to sourceRoot
generatorOpts	{}	An object containing the options to be passed down to the babel code generator, @babel/generator
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
highlightCode	true	ANSI highlight syntax error code frames
ignore	null	Opposite to the only option. ignore is disregarded if only is specified
inputSourceMap	null	A source map object that the output source map will be based on
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)
moduleId	null	Specify a custom name for module ids
moduleIds	false	If truthy, insert an explicit id for modules. By default, all modules are anonymous. (Not available for common modules)
moduleRoot	(sourceRoot)	Optional prefix for the AMD module formatter that will be prepend to the filename on module definitions
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
parserOpts	{}	An object containing the options to be passed down to the babel parser, babylon
plugins	[]	List of plugins to load and use
presets	[]	List of presets (a set of plugins) to load and use
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)
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
sourceFileName	(filenameRelative)	Set sources[0] on returned source map
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
sourceRoot	(moduleRoot)	The root from which all sources are relative
sourceType	"module"	Indicate the mode the code should be parsed in. Can be one of "script", "module", or "unambiguous". "unambiguous" will make Babel attempt to guess, based on the presence of ES6 import or export statements. Files with ES6 imports and exports are considered "module" and are otherwise "script".
wrapPluginVisitorMethod	null	An optional callback that can be used to wrap visitor methods. NOTE: This is useful for things like introspection, and not really needed for implementing anything. Called as wrapPluginVisitorMethod(pluginAlias, visitorType, callback).