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When Sagui was created, the frontend landscape was in a much different situation than it is today. Creating projects was a hell and we all faced the now infamous "JavaScript fatigue". Fast-forward to 2019 and we now have established solutions such as create-react-app that have a large community behind and is being well maintained. Therefore there is no longer a need for Sagui to exist.

This was a fantastic ride and I've learned a lot while building this little tool.

Thanks to all the community who help me along the way! ❤️🐒


Build Status Windows Tests npm version js-standard-style Join the chat at

Sagui is the single development dependency that provides the tooling required to build, test and develop modern JavaScript applications.

Its main goal is to kill the need of global CLIs and boilerplates, making a reproducible and easily updated environment across projects.

It follows an opinionated convention over configuration approach, providing a solid foundation so that you can focus on writing your code and not your tooling.

Quick start in 3 steps!

Let's create a new front-end project from scratch.

In a new folder, create a new npm project:

npm init -y

Install Sagui locally as a development dependency:

npm install --save-dev sagui

Start the development server:

npm start

Done! Sagui is an auto-bootstraping library, so during the install process (in a fresh npm project) it automatically creates a basic project scaffolding:

├── .editorconfig
├── .flowconfig
├── .gitignore
├── sagui.config.js
└── src
    ├── index.html
    ├── index.js
    ├── index.css
    └── index.spec.js

Just start writing the code inside the src/ folder.

npm scripts

Sagui manages the package.json scripts for you:

  • npm run build: build a development version of the project;
  • npm run dist: build an optimized (ready for deployment) version of the project;
  • npm run start: spin up a development server with live-reload and HMR;
  • npm run format: automatically format the code using prettier;
  • npm run test: run all test related scripts below;
  • npm run test:lint: run static analysis in the code;
  • npm run test:unit: run the unit tests;
  • npm run test:typecheck: run the static type analysis in the code;
  • npm run test:unit:watch: run a test watcher (great for development and debugging).

If you don't change the scripts, they will be automatically updated on new Sagui releases.


As stated earlier, Sagui strives to provide all the basic needs to create modern JavaScript applications.

Development server

The development server out-of-the-box has live reloading and hot-module replacement.


Sagui uses Webpack as its underlying bundling tool. The biggest feature that Webpack provides is that everything is a module. Sagui supports the following module types by default:

  • Fonts (.woff, .woff2, .ttf, .eot, .otf)
  • HTML (.html)
  • Images (.png, .jpg, .jpeg, .gif, .svg)
  • JavaScript (.js, .es6, .jsx) via Babel
  • JSON
  • Styles in CSS Modules in either plain CSS or Sass lang
  • Text (.txt) files loaded without any processing
  • Video (.ogg, .mp4)
  • YAML

During build, optimizations and special processing are also performed in the output bundle:

Testing and quality

Test automation in Sagui is achieved by creating .spec.js files inside the src/ folder using the Jasmine framework.

A simple example would be:

  • src/components/button.js
  • src/components/button.spec.js

Sagui will automatically run every test file that follows this convention.

Under the hood it uses Karma test runner to allow running the tests in the most diverse browsers and even through Selenium (not natively).

To run the tests Sagui uses Chrome Headless, but it fallbacks to PhantomJS if Chrome is not installed on the machine.

Make sure either of these browsers is installed to be able to run the tests:

To open the tests in a browser (or in multiple browsers!), simply follow the link Karma outputs when you start running the script test:unit:watch. Running them in a browser allows you to set breakpoints and debug your code properly. Note watch mode is necessary, else tests will stop running when finished.

Code formatting

We expect the code to be formatted using prettier. Sagui has a script that can apply the expected code format for you, simply run:

npm run format

To get the code formatted automatically for you, it is recommended that you install the prettier plugin in your editor of choice with the same configuration that is used by Sagui:

  • singleQuote: true
  • parser: babylon
  • semi: false
  • printWidth: 100
  • trailingComma: es5

Prettier is combined with the JavaScript Standard Style convention to check for common errors in the code.

Static type checking

Flowtype static type analysis is available as part of the testing suite. By default the flowtype checker only runs on files with the // @flow comment at the beginning, so no static type analysis will be actually performed unless you add that. See the docs for an more in depth explanation of why it is a good idea to have it like this.

Sagui bundles loose lib interface declarations for the Jasmine APIs used in the tests. You might want to look into the more complete flow-typed repo to get already made interfaces for common project dependencies such as React, Redux, Ramda, …


The Sagui configuration is all performed via the single sagui.config.js that is bootstraped in the project root folder once Sagui is first installed. At its simplest it could be just:

// sagui.config.js
module.exports = {
  pages: ['index']

Then we can add extra configuration on top of it:


These are static applications that can be built around multiple pages. Each page is the combination of an html and a js file.

// sagui.config.js
module.exports = {
  pages: ['index', 'about']

The previous configuration will expect and build the files:

  • src/about.html => dist/about.html
  • src/about.js => dist/about.js
  • src/index.html => dist/index.html
  • src/index.js => dist/index.js

Excluding a page from chunks

If you want a page to be excluded from either the vendor or common chunk, then you can do so by providing an object with a name and independent flag (set to true) instead of just the name of the page.

// sagui.config.js
module.exports = {
  pages: ['index', 'about', { name: 'demo', independent: true }]


If you want all your external dependencies (node_modules) in your pages to be bundled together in a "vendor" chunk, then set this flag to true. By default it is set to false.

// sagui.config.js
module.exports = {
  chunks: {
    vendor: true


If you do not want all the common dependencies of your pages to be bundled together in a "common" chunk, then set this flag to false. By default it is set to true.

// sagui.config.js
module.exports = {
  chunks: {
    common: false


Create reusable libraries that can be shared across applications. Sagui will take care of the build process so that external libraries are not bundled and that you have a CommonJS module as the output.

It works similarly to pages, allowing a list of "library entry points" to be built. The only difference here is that each library points to a single JavaScript file. Taking the example of a UI toolkit project, it could have the following libraries:

// sagui.config.js
module.exports = {
  libraries: ['button', 'field', 'select']

And these will build the files:

  • src/button.js => dist/button.js
  • src/field.js => dist/field.js
  • src/select.js => dist/select.js

Regarding external dependencies, Sagui will use the peerDependencies information in the project's package.json to determine what are the external dependencies of the library that shouldn't be bundled in the final build.

As an example, given a project with the package.json:

  "name": "library-project",
  "version": "1.0.0",
  "main": "index.js",
  "dependencies": {
    "left-pad": "1.1.0"
  "peerDependencies": {
    "react": "^0.14.7"

And somewhere in the source there are the following imports:

import React from 'react'
import leftPad from 'left-pad'

When building the project, react won't actually be bundled in the output but left-pad will, so your project won't blow up once left-pad is unpublished again.

Publishing libraries as UMD

If you need to build your library targeting UMD, you can use a slightly different configuration. For UMD you need to provide a umdName for the library, which is going to be the name that it will use to add itself to the window object when loaded as a global in the browser.

// sagui.config.js
module.exports = {
  libraries: [
      main: 'button',
      umdName: 'MyUIButton'


List of browsers using the browserslist format that the target build must support.

// sagui.config.js
module.exports = {
  browsers: [
    '> 1%',
    'last 2 versions',
    'IE 10'

If not provided, the above default will be used instead.

This information is used to decide:

  • JavaScript language features to transpile;
  • CSS prefixes to append.

Internally Sagui uses babel-preset-env and autoprefixer.


By default, styles compiled with Sagui will be output as CSS Modules, meaning they won't be global.

It is possible to disable this behavior and have regular CSS styles:

// sagui.config.js
module.exports = {
  style: {
    cssModules: false


Source maps are never generated for styles, but it is possible to enable it.

// sagui.config.js
module.exports = {
  style: {
    sourceMaps: true


By default, when building pages, Sagui extracts the CSS definitions into separated .css files. It is possible to disable this behavior and have the CSS inlined in the same JavaScript bundle.

// sagui.config.js
module.exports = {
  style: {
    extract: false


Dependencies installed through npm are not transpiled with Babel by default. If you have a dependency that needs to be transpiled it is very easy, just add its name to the list:

// sagui.config.js
module.exports = {
  javaScript: {
    transpileDependencies: ['dependency-to-be-transpiled']


By default, Flowtype ignores files that don't start with the // @flow comment line. If you want all your files to be statically type checked, you can enable that feature in the sagui config:

// sagui.config.js
module.exports = {
  javaScript: {
    typeCheckAll: true


Allow proxying requests to a separate, possible external, backend server.

// sagui.config.js
module.exports = {
  develop: {
    proxy: {
      '/some/path*': {
        target: '',
        secure: false

Please check node-http-proxy documentation for the available configuration options.

Escape hatches

If a build requirement can't be achieved via the previous configuration options, first open an issue so that we can add official support, and if you can't wait or is something very specific to your project, there is an escape hatch to allow extending the internal configurations.

These options are for advanced users that are familiar with how Webpack and Karma work.


Disable internal Sagui Webpack loaders in order to implement custom behavior via the additionalWebpackConfig.

// sagui.config.js
module.exports = {
  disableLoaders: ['yaml']

Possible values:

  • font
  • html
  • image
  • javaScript
  • style
  • txt
  • video
  • yaml


Extend the internal Webpack configuration using webpack-merge.

For example, It is possible to add additional Webpack plugins, like git-revision-webpack-plugin by:

// sagui.config.js
var GitRevisionPlugin = require('git-revision-webpack-plugin')

module.exports = {
  additionalWebpackConfig: {
    plugins: [
      new GitRevisionPlugin()

For more information about configuring Webpack, check the Webpack documentation.


Extend the internal Karma configuration.

As an example, let's change the default browser used to execute the tests from PhantomJS to Chrome. In the sagui.config.js file:

// sagui.config.js
module.exports = {
  additionalKarmaConfig: {
    browsers: ['Chrome']

For more information about configuring Karma, check the Karma documentation.


Invalid Host header - Accessing dev server from outside localhost

By default, Webpack disables access to the development server for hosts other than localhost, which means the development server will not be accessible from outside. If you want to give external access to the development server, you can set the develop.disableHostCheck to true:

// sagui.config.js
module.exports = {
  develop: {
    disableHostCheck: true

React Router

For react-router to work on the development server, an absolute static path for the output has to be configured on Webpack. You can do that by adding this configuration to sagui.config.js:

// sagui.config.js
module.exports = {
  additionalWebpackConfig: {
    output: {
      publicPath: '/'


Monkey artwork created by Ryan Spiering from the Noun Project.

Contributing and development

To develop the tool locally, we will need to resort to a combination of a global npm link and local links in projects.

You can start by linking Sagui globally. While at its folder:

npm link

The environment variable is to inform Sagui that it is working in a "linked environment".

Then, in the project you intend to use Sagui, link it locally:

npm link sagui

Now, the project is set to use your development copy of Sagui. Unfortunately, you will need to run any command in the project providing the environment variable SAGUI_LINK:

SAGUI_LINK=true npm start