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babel-core

Babel compiler core.

    6.26.3latestlerna-temp
    GitHub
    npm

Version published
Maintainers
6
Weekly downloads
8,353,448
increased by3.39%

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Package description

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'] });

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Readme

Source

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

OptionDefaultDescription
asttrueInclude the AST in the returned object
auxiliaryCommentAfternullAttach a comment after all non-user injected code.
auxiliaryCommentBeforenullAttach a comment before all non-user injected code.
babelrctrueSpecify whether or not to use .babelrc and .babelignore files. Not available when using the CLI, use --no-babelrc instead.
codetrueEnable code generation
commentstrueOutput 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"
extendsnullA path to an .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
getModuleIdnullSpecify 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.
highlightCodetrueANSI highlight syntax error code frames
ignorenullOpposite to the only option. ignore is disregarded if only is specified.
inputSourceMapnullA source map object that the output source map will be based on.
minifiedfalseShould the output be minified (not printing last semicolons in blocks, printing literal string values instead of escaped ones, stripping () from new when safe)
moduleIdnullSpecify a custom name for module ids.
moduleIdsfalseIf 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.
onlynullA 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.
retainLinesfalseRetain 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)
resolveModuleSourcenullResolve a module source ie. import "SOURCE"; to a custom value. Called as resolveModuleSource(source, filename).
shouldPrintCommentnullAn 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.
sourceMapsfalseIf 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".
wrapPluginVisitorMethodnullAn 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).

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Last updated on 27 Apr 2018

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