Integrating Reagent into JavaScript/React

WARNING: This won't be easy, you are about to marry together two separate realms.

What is it trying to achieve?

You want to start gradually using ClojureScript/Reagent in an existing JavaScript/React project.

Problems

1. How to export ClojureScript into JavaScript
2. How to share common dependencies (React, etc.) between ClojureScript/Reagent and JavaScript/React code
3. How to enable hot-reloading for ClojureScript code

Solving step by step

How to export ClojureScript into JavaScript

1. Bootstrap ClojureScript project and write your Reagent component
2. Use reagent.core/reactify-component to adapt Reagent component for usage with JS/React
3. Use ^:export meta on component's function to export it into a global scope (window object)
4. Put <script> tag referring ClojureScript output bundle into your HTML before JS project's script
5. Use Reagent components in your JS project

How to share common dependencies

In JavaScript project

1. In your JS project create a module that imports shared dependencies and exports them into global scope (window object)
2. Configure two builds (here using Webpack)
   • With an entry point with shared dependencies
   • With application entry point and shared dependencies configured as externals
3. Put <script> tag referring shared deps bundle into your HTML before ClojureScript project's script

In ClojureScript project

1. Exclude cljsjs/react and cljsjs/react-dom transitive dependencies from reagent dependency
2. Using :foreign-libs option alias react and react-dom with globally exported (from JS project) ones
   • :file is a required field in :foreign-libs, provide a path to an empty stub file
3. Set :infer-externs to true so that compiler can infer external references to shared deps

How to enable hot-reloading for ClojureScript code

On every change to ClojureScript source Figwheel will apply a patch to the code running in the browser. In order to reflect those changes on the screen you have to re-render the app so the new code will be executed.

In JavaScript project

• Export rendering function into global scope (window object)

In ClojureScript project

• Use ^:figwheel-hooks meta to enable Figwheel hooks and ^:after-load meta on a function that calls rendering function exported from JS