Allows you to build compile-time libraries
npm install babel-plugin-macrosAllows you to build simple compile-time libraries
---
[![Build Status][build-badge]][build]
[![Code Coverage][coverage-badge]][coverage]
[![version][version-badge]][package]
[![downloads][downloads-badge]][npmtrends]
[![MIT License][license-badge]][license]
[![All Contributors][all-contributors-badge]](#contributors-)
[![PRs Welcome][prs-badge]][prs]
[![Code of Conduct][coc-badge]][coc]
Check out
this guest post
on the Babel.js blog for a complete write up on the problem, motivation, and
solution.
Currently, each babel plugin in the babel ecosystem requires that you configure
it individually. This is fine for things like language features, but can be
frustrating overhead for libraries that allow for compile-time code
transformation as an optimization.
babel-plugin-macros defines a standard interface for libraries that want to use
compile-time code transformation without requiring the user to add a babel
plugin to their build system (other than babel-plugin-macros, which is ideally
already in place).
For instance, many css-in-js libraries have a css tagged template string
function:
``js
const styles = css
.red {
color: red;
}`
The function compiles your css into (for example) an object with generated class
names for each of the classes you defined in your css:
`js`
console.log(styles) // { red: "1f-d34j8rn43y587t" }
This class name can be generated at runtime (in the browser), but this has some
disadvantages:
- There is cpu usage/time overhead; the client needs to run the code to generate
these classes every time the page loads
- There is code bundle size overhead; the client needs to receive a CSS parser
in order to generate these class names, and shipping this makes the amount of
js the client needs to parse larger.
To help solve those issues, many css-in-js libraries write their own babel
plugin that generates the class names at compile-time instead of runtime:
`js
// Before running through babel:
const styles = css
.red {
color: red;
}`
// After running through babel, with the library-specific plugin:
const styles = {red: '1f-d34j8rn43y587t'}
If the css-in-js library supported babel-plugin-macros instead, then they
wouldn't need their own babel plugin to compile these out; they could instead
rely on babel-plugin-macros to do it for them. So if a user already had
babel-plugin-macros installed and configured with babel, then they wouldn'tbabel-plugin-macros
need to change their babel configuration to get the compile-time benefits of the
library. This would be most useful if the boilerplate they were using came with out of the box, which is true forcreate-react-app
[][cra].
Although css-in-js is the most common example, there are lots of other things
you could use babel-plugin-macros for, like:
- Compiling GraphQL fragments into objects so that the client doesn't need a
GraphQL parser
- Eval-ing out code at compile time that will be baked into the runtime code,
for instance to get a list of directories in the filesystem (see
[preval][preval])
- Installation
- Usage
- User docs
- Author docs
- Caveats
- FAQ
- How do I find available macros?
- What's the difference between babel plugins and macros?
- In what order are macros executed?
- Does it work with function calls only?
- How about implicit optimizations at compile time?
- Inspiration
- Other Solutions
- Issues
- π Bugs
- π‘ Feature Requests
- Contributors β¨
- LICENSE
This module is distributed via [npm][npm] which is bundled with [node][node] and
should be installed as one of your project's devDependencies:
``
npm install --save-dev babel-plugin-macros
> You may like to watch
> this YouTube video
> to get an idea of what macros is and how it can be used.
Are you trying to use babel-plugin-macros? Go toother/docs/user.md.
Are you trying to make your own macros that works with babel-plugin-macros? Goother/docs/author.md
to . (you should probably read the
user docs too).
#### Babel cache problem
> Note: This issue is not present when used in Create React App.
Most of the time you'll probably be using this with the babel cache enabled in
webpack to rebuild faster. If your macro function is not pure which gets
different output with same code (e.g., IO side effects) it will cause recompile
mechanism fail. Unfortunately you'll also experience this problem while
developing your macro as well. If there's not a change to the source code that's
being transpiled, then babel will use the cache rather than running your macro
again.
For now, to force recompile the code you can simply add a cache busting comment
in the file:
`diff
import macro from 'non-pure.macro';
-// Do some changes of your code or
+// add a cache busting comment to force recompile.
macro('parameters');
`
This problem is still being worked on and is not unique to
babel-plugin-macros. For more details and workarounds, please check related
issues below:
- babel-plugin-preval:
How to force recompile? #19
- graphql.macro:
Recompile problem (babel cache) #6
- twin.macro:
Can't change taliwind config #37
You can write your own without publishing them to npm, but if you'd like to
see existing macros you can add to your project, then take a look at the
Awesome babel macros
repository.
Please add any you don't see listed!
Let's use
babel-plugin-console as
an example.
If we used babel-plugin-console, it would look like this:
1. Add babel-plugin-console to .babelrc
2. Use it in a code:
`js
function add100(a) {
const oneHundred = 100
console.scope('Add 100 to another number')
return add(a, oneHundred)
}
function add(a, b) {
return a + b
}
`
When that code is run, the scope function does some pretty nifty things:
Browser:
!Browser console scoping add100
Node:

Instead, let's use the macro it's shipped with like this:
1. Add babel-plugin-macros to .babelrc (only once for all macros)
2. Use it in a code:
`js
import scope from 'babel-plugin-console/scope.macro'
function add100(a) {
const oneHundred = 100
scope('Add 100 to another number')
return add(a, oneHundred)
}
function add(a, b) {
return a + b
}
`
The result is exactly the same, but this approach has a few advantages:
Advantages:
- requires only one entry in .babelrc for all macros used in project. Add thatbabel-plugin-macros
once and you can use all the macros you want
- toolkits (like [create-react-app][cra]) may already support
, so no configuration is needed at allconsole.scope
- it's explicit. With people may be fooled that it's just aconsole
normal API when there's really a babel transpilation going on. Whenscope
you import , it's obvious that it's macro and does something with thebabel-plugin-console
code at compile time. Some ESLint rules may also have issues with plugins that
look for "global" variables
- macros are safer and easier to write, because they receive exactly the AST
node to process
- If you misconfigure you wont find out until you run thebabel-plugin-macros
code. If you misconfigure you'll get a compile-time
error.
Drawbacks:
- Cannot (should not) be used for implicit transpilations (like syntax plugins)
- Explicitness is more verbose. Which some people might consider a drawback...
This is another advantage of babel-plugin-macros over regular plugins. The
user of the macro is in control of the ordering! The order of execution is the
same order as imported. The order of execution is clear, explicit and in full
control of the user:
`js
import preval from 'preval.macro'
import idx from 'idx.macro'
// preval macro is evaluated first, then idx
`
This differs from the current situation with babel plugins where it's
prohibitively difficult to control the order plugins run in a particular file.
No! Any AST node type is supported.
It can be tagged template literal:
`js7 * 6
import eval from 'eval.macro'
const val = eval`
A function:
`js`
import eval from 'eval.macro'
const val = eval('7 * 6')
JSX Element:
`js`
import Eval from 'eval.macro'
const val =
Really, anything...
See the testing snapshot for more
examples.
All examples above were _explicit_ - a macro was imported and then evaluated
with a specific AST node.
Completely different story are _implicit_ babel plugins, like
transform-react-constant-elements,
which process whole AST tree.
Explicit is often a better pattern than implicit because it requires others to
understand how things are globally configured. This is in this spirit are
babel-plugin-macros designed. However, some things _do_ need to be implicit,
and those kinds of babel plugins can't be turned into macros.
- threepointone/babel-plugin-macros
- [facebookincubator/create-react-app#2730][cra-issue]
Thank you to @phpnode for donating the npm package
babel-plugin-macros`.
- sweetjs
_Looking to contribute? Look for the [Good First Issue][good-first-issue]
label._
Please file an issue for bugs, missing documentation, or unexpected behavior.
[See Bugs][bugs]
Please file an issue to suggest new features. Vote on feature requests by adding
a π. This helps maintainers prioritize what to work on.
[See Feature Requests][requests]
Thanks goes to these people ([emoji key][emojis]):
This project follows the [all-contributors][all-contributors] specification.
Contributions of any kind welcome!
MIT
[npm]: https://www.npmjs.com
[node]: https://nodejs.org
[build-badge]: https://img.shields.io/github/workflow/status/kentcdodds/babel-plugin-macros/validate?logo=github&style=flat-square
[build]: https://github.com/kentcdodds/babel-plugin-macros/actions?query=workflow%3Avalidate
[coverage-badge]: https://img.shields.io/codecov/c/github/kentcdodds/babel-plugin-macros.svg?style=flat-square
[coverage]: https://codecov.io/github/kentcdodds/babel-plugin-macros
[version-badge]: https://img.shields.io/npm/v/babel-plugin-macros.svg?style=flat-square
[package]: https://www.npmjs.com/package/babel-plugin-macros
[downloads-badge]: https://img.shields.io/npm/dm/babel-plugin-macros.svg?style=flat-square
[npmtrends]: http://www.npmtrends.com/babel-plugin-macros
[license-badge]: https://img.shields.io/npm/l/babel-plugin-macros.svg?style=flat-square
[license]: https://github.com/kentcdodds/babel-plugin-macros/blob/main/LICENSE
[prs-badge]: https://img.shields.io/badge/PRs-welcome-brightgreen.svg?style=flat-square
[prs]: http://makeapullrequest.com
[coc-badge]: https://img.shields.io/badge/code%20of-conduct-ff69b4.svg?style=flat-square
[coc]: https://github.com/kentcdodds/babel-plugin-macros/blob/main/CODE_OF_CONDUCT.md
[emojis]: https://github.com/all-contributors/all-contributors#emoji-key
[all-contributors]: https://github.com/all-contributors/all-contributors
[all-contributors-badge]: https://img.shields.io/github/all-contributors/kentcdodds/babel-plugin-macros?color=orange&style=flat-square
[bugs]: https://github.com/kentcdodds/babel-plugin-macros/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aopen+sort%3Acreated-desc+label%3Abug
[requests]: https://github.com/kentcdodds/babel-plugin-macros/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc+label%3Aenhancement
[good-first-issue]: https://github.com/kentcdodds/babel-plugin-macros/issues?utf8=%E2%9C%93&q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc+label%3Aenhancement+label%3A%22good+first+issue%22
[preval]: https://github.com/kentcdodds/babel-plugin-preval
[cra]: https://github.com/facebook/create-react-app
[cra-issue]: https://github.com/facebook/create-react-app/issues/2730