esm
The brilliantly simple, babel-less, bundle-less ECMAScript module loader.
esmis the world’s most advanced ECMAScript module loader.
This fast, production ready, zero dependency loader is all you need to support
ECMAScript modules in Node 6+. See the release post
and video for details!
Install
-
New projects
Run
npm init esmoryarn create esm.:bulb: Use the
-yflag to answer “yes” to all prompts. -
Existing projects
Run
npm i esmoryarn add esm.
Getting started
There are two ways to enable esm.
-
Enable
esmfor packages:Use
esmto load the main ES module and export it as CommonJS.index.js
// Set options as a parameter, environment variable, or rc file. require = require("esm")(module/*, options*/) module.exports = require("./main.js")main.js
// ESM syntax is supported. export {}:bulb: These files are automagically created with
npm init esmoryarn create esm. -
Enable
esmfor local runs:node -r esm main.js:bulb: Omit the filename to enable
esmin the REPL.
Features
:clap: By default, :100: percent CJS interoperability is enabled so you can get stuff done.
:lock: .mjs files are limited to basic functionality without support for esm options.
Out of the box esm just works, no configuration necessary, and supports:
- Passing all applicable test262 compliance tests
import/exportimport.meta- Dynamic
import - Live bindings
- File URI scheme
- Node
stdin,--eval,--printflags - Node
--checkflag (Node 10+)
Options
Specify options with one of the following:
"esm"field inpackage.json- CJS/ESM in an
.esmrc.js,.esmrc.cjs, or.esmrc.mjsfile - JSON6 in an
.esmrcor.esmrc.jsonfile - JSON6 or file path in the
ESM_OPTIONSenvironment variable ESM_DISABLE_CACHEenvironment variable
DevOpts
Tips
Bundling
-
For bundlers like
browserify+esmify,
parcel-bundler, andwebpack
add a"module"field topackage.jsonpointing to the main ES module."main": "index.js", "module": "main.js":bulb: This is automagically done with
npm init esmoryarn create esm.
Extensions
- Enable
esmforwallaby.jsfollowing their
integration example.
Loading
-
Load
esmbefore loaders/monitors like
@babel/register,
newrelic,
sqreen, and
ts-node. -
Load
esmforjasmineusing the
"helpers"
field injasmine.json:"helpers": [ "node_modules/esm" ] -
Load
esmwith “node-args" options of:pm2:--node-args="-r esm"
-
Load
esmwith “require” options of
ava,
mocha,
nodemon,
nyc,
qunit,
tape, and
webpack.:bulb: Builtin
requirecannot sideload.mjsfiles. However,.jsfiles
can be sideloaded or.mjsfiles may be loaded with dynamicimport.