Externs are needed by the Closure Compiler. ClojureScript produces them by default.

For 3rd party JS libraries, we need to create them.

http://cljsjs.github.io/ provides some pre-bundled stuff, including externs:

• React
• leaflet
• react-leaflet

There is also an :infer-externs true compiler flag. This is black magic and may not work.

We also need to set (set! *warn-on-infer* true) in the files where we use a 3rd party JS library.

Then, if we see any warnings, we can provide a type hint to finish off.

If this gets complicated, we should write out own externs file.

This contains globals like js/Infinity and js/undefined.

Uses JavaScript equality.

Ratio, BigDecimal, BigInteger not supported.

Different in complicated ways.

Every namespace matches a file.

There is a separate macro expansion phase.

FigWheel is a nice debugging in the browser thing for ClojureScript.

It starts a web server, and automatically hot-reloads the browser page as your modify your ClojureScript.

You need to add the lein-figwheel plugin in your project.clj.

Then you can run lein figwheel to start the server.

It depends on you writing your ClojureScript files such that they can be reloaded.

M-x cider-jack-in-clojurescript

Also, maybe it can work with Figwheel? Not sure if any integration is actually needed there?