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ES6 in Node and in your Browser with Traceur

How to make it work in node

Install traceur and save it to your package.json.

npm install traceur --save

Add the following code to your node entry point, in my case server.js. This will transpile required files to valid ES5 syntax on the fly but ignores your dependencies to not spend time transpiling those.

var traceur = require("traceur");
traceur.require.makeDefault(function (filename) {
// don't transpile our dependencies, just our app
return filename.indexOf("node_modules") === -1;

Start the server with node server.js and enjoy the new features.

How to make it work in the browser

It makes sense to transpile your app into a ES5 javascript file once, which is then loaded by a browser in order to not have users waiting for the transpiling process every time. For that I like to use webpack and the traceur-loader package:

npm install --save-dev webpack traceur-loader

Create a webpack.config.js, here I'm using a different entry point src/web/app.js which should be loaded. Webpack will automatically include all required dependencies in the resulting javascript bundle. The most interesting line is the loader definition where all javascript files in the src directory will be run through traceur.

module.exports = {
entry: {
bundle: "./src/web/app.js",
output: {
path: "build/js",
filename: "[name].js",
module: {
loaders: [
test: /src\/.*\.js$/,
loader: "traceur?experimental=true&runtime=true",

For development I recommend running webpack with the -d flag which generates source maps and the --watch flag to recompile changed files incrementally.

node_modules/.bin/webpack --config webpack.config.js --watch -d --progress

The resulting ES5 javascript file will be in build/js/bundle.js and can be included in a browser:

<script src="build/js/bundle.js" />

See a list of possible language features.

© 2022 by Adrian Philipp