babel-core

What is babel-core?

The babel-core package is a part of Babel, a JavaScript compiler that allows developers to use next-generation JavaScript, today. It transforms ES6, ES7, and beyond into backwards compatible versions of JavaScript that can be run on older browsers and environments. It also allows for the use of JSX, Flow, TypeScript, and other features not natively supported in all environments.

What are babel-core's main functionalities?

Code Transformation

Transforms ES6/ES7 code to ES5. This is useful for compatibility with older browsers and environments.

babel.transform('code();', options);

File Transformation

Synchronously transforms the entire contents of a file. Useful for build processes.

babel.transformFileSync('filename.js', options);

AST Generation

Parses code to its Abstract Syntax Tree (AST) representation, which can be used for analysis or modification of the code.

babel.parse('code();', options);

Plugin/Preset Application

Applies Babel plugins and presets to the code, allowing for custom transformations and feature sets.

babel.transform('code();', { plugins: ['plugin-name'], presets: ['preset-name'] });

Other packages similar to babel-core

typescript

TypeScript is a superset of JavaScript that compiles to plain JavaScript. It offers type checking and is aimed at the development of large applications. It is similar to Babel in that it processes modern JavaScript features, but it also introduces its own syntax and type system.

esbuild

Esbuild is an extremely fast JavaScript bundler and minifier. It also transpiles code, similar to Babel, but it focuses on build performance and speed, often outperforming Babel in these aspects.

swc

SWC is a super-fast compiler written in Rust that functions similarly to Babel. It focuses on speed and also offers minification. SWC can be a drop-in replacement for Babel in many cases, offering faster build times.

README

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)

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

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

Example

var result = babel.transform("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)

Given an AST, transform it.

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

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
ast	true	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
babelrc	true	Specify whether or not to use .babelrc and .babelignore files. Not available when using the CLI, use --no-babelrc instead
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 environment 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"
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)
resolveModuleSource	null	Resolve a module source ie. import "SOURCE"; to a custom value. Called as resolveModuleSource(source, filename)
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
sourceMapTarget	(filenameRelative)	Set file on returned source map
sourceRoot	(moduleRoot)	The root from which all sources are relative
sourceType	"module"	Indicate the mode the code should be parsed in. Can be either "script" or "module"
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).