Babel Core
Babel core is the API. For v5 the babel package is the CLI and depends on babel-core. For v6, the babel-cli package is the CLI (the CLI bin command is still babel though) and the babel package doesn’t do anything. Babel-runtime I guess is just the runtime (polyfill and helpers) to support code that’s already been transformed.
var babel = require("@babel/core");
import { transform } from "@babel/core";
import * as babel from "@babel/core";
All transformations will use your local configuration files.
Transform
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.
transformSync
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;
transformAsync
babel.transformAsync(code: string, options?: Object)
Transforms the passed in code. Returning an promise for an object with the generated code, source map, and AST.
babel.transformAsync(code, options) // => Promise<{ code, map, ast }>
Example
babel.transformAsync("code();", options).then(result => {
result.code;
result.map;
result.ast;
});
transformFile
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 }
});
transformFileSync
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;
transformFileAsync
babel.transformFileAsync(filename: string, options?: Object)
Promise version of babel.transformFile. Returns a promise for the transformed contents of the filename.
babel.transformFileAsync(filename, options) // => Promise<{ code, map, ast }>
Copy
Example
babel.transformFileAsync("filename.js", options).then(result => {
result.code;
});
Copy
transformFromAst
babel.transformFromAst(ast: Object, code?: string, options?: Object, callback: Function): FileNode | null
Given an AST, transform it.
const sourceCode = "if (true) return;";
const parsedAst = babel.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.
transformFromAstSync
babel.transformFromAstSync(ast: Object, code?: string, options?: Object)
Given an AST, transform it.
const sourceCode = "if (true) return;";
const parsedAst = babel.parse(sourceCode, { allowReturnOutsideFunction: true });
const { code, map, ast } = babel.transformFromAstSync(parsedAst, sourceCode, options);
transformFromAstAsync
babel.transformFromAstAsync(ast: Object, code?: string, options?: Object)
Given an AST, transform it.
const sourceCode = "if (true) return;";
babel.parseAsync(sourceCode, { allowReturnOutsideFunction: true })
.then(parsedAst => {
return babel.transformFromAstSync(parsedAst, sourceCode, options);
})
.then(({ code, map, ast }) => {
// ...
});
parse
babel.parse(code: string, options?: Object, callback: Function)
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.
Compat Note:
In Babel 7’s early betas, this method was synchronous and parseSync did not exist. For backward-compatibility, this function will behave synchronously if no callback is given. If you’re starting with Babel 7 stable and need synchronous behavior, please use parseSync since this backward-compat may be dropped in future major versions of Babel.
parseSync
babel.parseSync(code: string, options?: Object)
Returns an AST.
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.
parseAsync
babel.parseAsync(code: string, options?: Object)
Returns a promise for an AST.
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.
loadOptions
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.
loadPartialConfig
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 file-relative configuration file, if there was one.
- babelignore: string | void – The path of the .babelignore file, if there was one.
- config: string | void – The path of the project-wide config file 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. Options 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.
createConfigItem
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
- Primary options
- Config Loading options
- Plugin and Preset configuration
- Config Merging options
- Source Map options
- Misc options
- Code Generator options
- AMD / UMD / SystemJS options
- Option concepts
Options can be passed to Babel in a variety of ways. When passed directly to Babel, you can just pass the objects object. When Babel is used via a wrapper, it may also be necessary, or at least more useful, to pass the options via configuration files.
If passing options via @babel/cli you’ll need to kebab-case the names. i.e.
npx babel --root-mode upward file.js # equivalent of passing the rootMode config option