Working with the Merlin UI

This file explains how to work with the React-based Merlin UI.

Introduction

The React-based Merlin UI was bootstrapped using Create React App, a popular toolkit for generating React application setups. You can find general information about Create React App on their documentation site.

Development environment

To work with the React UI code, you will need to have the following tools installed:

• The Node.js JavaScript runtime.
• The Yarn package manager.

Installing npm dependencies

The React UI depends on a large number of npm packages. These are not checked in, so you will need to download and install them locally via the Yarn package manager:

yarn

Yarn consults the package.json and yarn.lock files for dependencies to install. It creates a node_modules directory with all installed dependencies.

Running a local development server

You need to set the REACT_APP_OAUTH_CLIENT_ID in .env.development with the Google Oauth Client ID for authentication.

Then, you can start a development server for the React UI outside of a running Merlin server by running:

yarn start

This will open a browser window with the React app running on http://localhost:3000/. The page will reload if you make edits to the source code. You will also see any lint errors in the console.

Due to a "proxy": "http://localhost:8080/v1" setting in the package.json file, any API requests from the React UI are proxied to localhost on port 8080 by the development server. This allows you to run a normal Merlin server to handle API requests, while iterating separately on the UI.

[browser] ----> [localhost:3000 (dev server)] --(proxy API requests)--> [localhost:8080/v1 (Merlin)]

Linting

We use lint-staged for the linter. To detect and automatically fix lint errors against staged git files, run:

yarn lint

This is also available via the lint-ui target in the main Merlin Makefile.

Building the app for production

To build a production-optimized version of the React app to a build subdirectory, run:

yarn build

NOTE: You will likely not need to do this directly. Instead, this is taken care of by the build target in the main Merlin Makefile when building the full binary.

Integration into Merlin

To build a Merlin binary that includes a compiled-in version of the production build of the React app, change to the root of the repository and run:

make build

This installs npm dependencies via Yarn, builds a production build of the React app, and then finally compiles in all web assets into the Merlin binary.