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@babel/core
Advanced tools
@babel/core is the core library of the Babel JavaScript compiler. It is primarily used for transforming ES6+ code into backwards compatible JavaScript that can be run by older JavaScript engines. Babel is widely used for its ability to transpile new JavaScript syntax, JSX, TypeScript, and for its plugin system that allows developers to use experimental features and customize the build process.
Syntax Transformation
Transforms modern JavaScript syntax into a backwards compatible version. For example, it can convert ES6 arrow functions into regular ES5 functions.
require('@babel/core').transform('code', { presets: ['@babel/preset-env'] });
Plugin/Preset Application
Applies Babel plugins or presets to the code to enable specific transformations or sets of transformations.
require('@babel/core').transform('code', { plugins: ['@babel/plugin-transform-arrow-functions'] });
Source Map Generation
Generates source maps which help in debugging the original source code after it has been transformed by Babel.
require('@babel/core').transform('code', { sourceMaps: true });
Code Generation
Generates code from an Abstract Syntax Tree (AST). This is useful when you want to transform the AST directly or manipulate it before generating code.
require('@babel/core').transformFromAst(ast, 'code', { presets: ['@babel/preset-env'] });
TypeScript is a superset of JavaScript that compiles to plain JavaScript. It offers type checking and is aimed at the development of large applications. While it does transpile code, it is more focused on type safety and less on new syntax features.
esbuild is an extremely fast JavaScript bundler and minifier. It also provides a limited set of transformation features, such as JSX and TypeScript support. It is not as extensible as Babel but is focused on speed and efficiency.
swc is a super-fast compiler written in Rust that aims to be a drop-in replacement for Babel. It supports most of the modern JavaScript features and is focused on performance. It is gaining popularity in the JavaScript community for its speed.
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.
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;
});
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.
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;
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 }
});
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;
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;
});
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.
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 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 |
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 |
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 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 import s and export s 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) . |
FAQs
Babel compiler core.
The npm package @babel/core receives a total of 50,075,341 weekly downloads. As such, @babel/core popularity was classified as popular.
We found that @babel/core demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 4 open source maintainers collaborating on the project.
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