This is a Babel plugin that transpiles tagged regex
templates into native RegExp
literals, enabling syntax for modern and more readable regex features (atomic groups, subroutines, insignificant whitespace, comments, etc.) without the need for calling regex
at runtime. Although regex
is already a lightweight and high-performance library, this takes things further by giving you its developer experience benefits without adding any runtime dependencies and without users paying any runtime cost.
Input:
const ipv4 = regex`
^ \g<byte> (\.\g<byte>){3} $
(?(DEFINE)
(?<byte> 2[0-4]\d | 25[0-5] | 1\d\d | [1-9]?\d)
)
`;
Output:
const ipv4 = /^(?:2[0-4]\d|25[0-5]|1\d\d|[1-9]?\d)(?:\.(?:2[0-4]\d|25[0-5]|1\d\d|[1-9]?\d)){3}$/v;
The following call formats are all supported:
regex`<expression>`
regex()`<expression>`
regex('<flags>')`<expression>`
regex({<options>})`<expression>`
Interpolation into the expression is supported, so long as the interpolated values are:
- Inline string, regexp, or number literals.
- Inline regexes constructed via
RegExp
ornew RegExp
with string values. - Inline patterns, via
pattern`…`
as a template tag (without interpolation) orpattern(…)
as a funcion call with a string or number literal as the value.
Additional details:
- Wherever strings are allowed,
'…'
,"…"
,`…`
, andString.raw`…`
can all be used, so long as they don't include interpolation.
- Tagged
regex
templates that interpolate variables or other dynamic values are not transformed. - The specific
regex
optionssubclass
,plugins
, andunicodeSetsPlugin
are unsupported. Regexes that use these options are not transformed. - Calling the
regex
tag as a function instead of with backticks is not transformed.
The following options are available when running the Babel plugin:
-
removeImport
— Iftrue
, removes any import declarations with module name'regex'
. -
disableUnicodeSets
— Iftrue
, addsregex
optiondisable: {v: true}
to all regexes before transformation. -
optimize
(experimental) — Iftrue
, attempts to further optimize the regex source generated byregex
.- Uses an external library (regexp-tree's optimizer) that doesn't support flag-v-only syntax and isn't fully context-aware, so you should check the output.
-
headerComment
— If given a value, it will be added in a comment at the top of processed output/files.
By default, the regex
tag implicitly adds flag v (unicodeSets
, supported by Node.js 20 and 2023-era browsers) to generated regexes, but it automatically switches to flag u (while applying v's escaping rules) in environments without native v support. This creates an issue for the Babel plugin, because although it will typically be run in environments that support flag v, the transpiled results may need to run for users in old browsers without native v.
There are several ways to address this:
-
Option 1: Leave v enabled and transpile v with a separate Babel plugin.
- This allows supporting v-only syntax (like nested character classes) in older environments.
- Use Babel's official plugin @babel/plugin-transform-unicode-sets-regex, which is also included in @babel/preset-env.
-
Option 2: Disable v for all transpiled regexes.
- To do this, set the Babel plugin option
disableUnicodeSets: true
(see details above). - This keeps things simple/clean and avoids a second regex transpilation step.
- This doesn't support the use of v-only syntax.
- To do this, set the Babel plugin option
-
Option 3: Disable v for individual regexes.
- To do this, use the
regex
optionregex({disable: {v: true}})`…`
in your code. - This maintains 100% parity between code running with or without the Babel plugin.
- This doesn't support the use of v-only syntax.
- To do this, use the
You can try all these options in the demo REPL.
Add this plugin and a recent version of Babel (tested with v7.24) to your project:
npm install --save-dev @babel/core @babel/cli
npm install --save-dev babel-plugin-transform-regex
Run the following command to compile all of your code from the src
directory to lib
:
./node_modules/.bin/babel src --out-dir lib --plugins=babel-plugin-transform-regex
To make this easier to run, create a config file in the root of your project named babel.config.json
, with this content:
{
"plugins": ["babel-plugin-transform-regex"]
}
Or to set plugin options:
{
"plugins": [["babel-plugin-transform-regex", {"removeImport": true}]]
}
Then add a script to your package.json
to run the build:
"scripts": {
"build": "babel src --out-dir lib"
}
After that, you can run it via npm run build
.