# re-frame-trace

A trace window for re-frame

## Motivation

re-frame provides a data driven architecture, but we need to be able to inspect it. re-frame-trace takes inspiration from [redux-devtools](https://github.com/gaearon/redux-devtools), and provides several ways to visualise the structure and state of your re-frame application.

<img src="docs/images/trace-window.png" height="400px">

## How does it work?

re-frame has instrumentation to collect traces throughout various important points in the lifecycle of a re-frame app. re-frame-trace is a consumer of these traces, and provides visualisations of the traces. These traces have a well-defined structure, and will eventually be standardised, allowing other developers to create their own tooling to work against the traces. Currently, re-frame's tracing and re-frame-trace are in alpha and are subject to change at any time. Caveat usor [sic].

## Getting started

There are two requirements to use re-frame-trace:

1. Compile your app with `:closure-defines: "re_frame.trace.trace_enabled_QMARK_" true` and `:preloads [day8.re-frame.trace.preload]`, e.g.

    ```cljs
    {:builds
       [{:id           "dev"
         :source-paths ["src" "dev"]
         :compiler     {...
                        :closure-defines      {"re_frame.trace.trace_enabled_QMARK_" true}
                        :preloads             [day8.re-frame.trace.preload]}}]}
    ```

    By default, re-frame tracing is compiled out, so it won't impose a performance cost in production. The trade-off here is that you need to explicitly enable it in development.

    The [preloads](https://github.com/clojure/clojurescript/wiki/Compiler-Options#preloads) option (`:preloads [day8.re-frame.trace.preload]`) has to be set in order to automatically monkeypatch Reagent to add appropriate lifecycle hooks. Yes this is gross, and yes we will try and make a PR to reagent to add proper hooks, once we know exactly what we need.
2. In your app's view code, add in `day8.re-frame.trace/devtools` as a sibling to the root application view. For example, if your app looks like this:

   ```cljs
   (defn main []
     [re-com/v-box
       ;; your app here
       ])

   (defn ^:export start-app
     []
     (myapp.boot/init!)
     (reagent/render (fn [] [main]) (.getElementById js/document "app")))
   ```

   then you need to modify `main` to look something like:

   ```cljs
   (defn main []
     [:div
       [re-com/v-box
         ;; your app here
         ]
       [trace/devtools]) ;; day8.re-frame.trace is aliased is trace
   ```

Now you can start up your application. Once it is loaded, press Ctrl+H to slide open the trace panel and enable tracing. When the panel is closed, tracing is disabled.