re-frame-trace

re-frame-trace let's you look at the inner workings of a running re-frame application. It presents as a programmer's dashboard, delivering curated insight and illumination. Your capacity to debug will increase because you know more.

It Is Epoch Oriented

re-frame applications are computationally regular. First an event happens, and then boom, boom, boom go a series of known computational steps (aka dominoes), in a known order. When this chain reaction completes, a re-frame app enters a quiescent state waiting for another event to kick off the next iteration of the same process.

Each re-frame event and its consequent computation forms a bounded "epoch" which can be inspected, analysed and understood independently of other epochs. This tool is epoch-oriented - it shows you one at a time.

And, yes, it has "time travel debugger" capabilities - you can go backwards and forwards through epochs - but that's really not the most interesting or powerful aspect of what re-frame-trace delivers.

It Is About Trace Data

As it runs, re-frame logs "trace" as data (not strings). This data trace provides an x-ray of your app's functioning.

re-frame-trace is essentially a consumer, processor and displayer of this x-ray trace data.

It Is About The Data Flow

While re-frame is a functional framework, it is strongly defined by its "data oriented" design. re-frame "flows" data, in a loop, through the functions you provide. To understand what is happening in a re-frame app, you must understand what data is "happening".

So, data is at the core of re-frame-trace in both of the ways just described, and data is a powerful and leverageable substrate.

Think about it ... every single time you put a printlin into your program, you are printing out what? Obvserving data is how you figure out what's going on.

It Is A Data Dashboard

Except, there's often too much data - you can drown in the detail.

So, re-frame-trace tries to be a "dashboard" which curates this "raw data" into "information" through various kinds of analysis and "roll ups". It should deliver insight "at a glance", while still allowing you to drill down into the detail.

Which Is Helpful How?

Four ways:

1. It helps you to learn re-frame. Simply looking at the "raw traces" provides insight into how it operates. Even experienced re-framians, er, like me, have learned a lot.

2. It helps you to explore and learn an unfamiliar re-frame codebase. When I click, over here, on this "X" button, it shows me what event is dispatch-ed and in what namespace the associated event handler is registered. And, "oh look, that's interesting - four subscriptions recalculated". Etc.

3. It helps you with debugging. You see an x-ray of your app's functioning. In particular, it will assist you to write and debug event handlers, which is useful because they hold most of the logic in your re-frame apps.

4. It helps you to find performance problems and/or detect where there is unnecessary computation occurring.

Deeper knowledge is the goal. Easier debugging is the symptom.

Temporary Warning

Some of the claims above are aspirational. re-frame-trace remains a WIP experiment. But we're getting there.

A Visual Sampler

Installation

If you are using leiningen, modify project.clj in the following ways. When puzzling over the various possible leiningen configurations, it's often helpful to look at a sample project.clj.

• Update your re-frame dependency to at least 0.10.4 - [re-frame "0.10.4"].

• Add re-frame-trace as a dev dependency by placing [day8.re-frame/trace "VERSION"] within :profiles :dev :dependencies. For example:

  :profiles
     {:dev
        {:dependencies [[some-other-package  "0.0.0"]
                        [day8.re-frame/trace "0.0.0 (see version above)"]] }}
  

  If your project uses React 16 and Reagent 0.8.0-alpha2 (or higher) then you will need to add the qualifier -react16 to the version, e.g. [day8.re-frame/trace "0.0.0-react16"].

• Locate the :compiler map under :dev and add:

  • :closure-defines {"re_frame.trace.trace_enabled_QMARK_" true}
  • :preloads [day8.re-frame.trace.preload]

  For example:

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

cljs-devtools is not required to use re-frame-trace, but it is highly recommended.

Usage

• Make sure you have followed all of the installation instructions above.

• Start up your application.

• Once it is loaded, focus the document window and press ctrl-h to slide open the trace panel and enable tracing.

• When the panel is closed, tracing is disabled.

Use Cases

app-db

• Inspect a portion of app-db's state with the path inspector, allowing you to focus on just the parts you care about.
• Reset app-db to before an event was run to run it again, instead of resetting the whole application
• Toggle app-db before and after states for running an event, to inspect UI changes.

Timing

• Answer the question "Why is my app slow when it runs this event?"
• See whether time is spent in processing an event, or rendering the changes

Troubleshooting

• Try a lein clean
• Make sure you have followed all the installation steps.

If re-frame-trace throws an exception on startup

• Reset the settings to factory defaults in the settings panel
• If you can't load the settings panel, run day8.re_frame.trace.factory_reset_BANG_() in the JavaScript console.
• If neither of those work, remove all of the keys with the prefix day8.re-frame.trace from your browser's Local Storage.

How does it work?

re-frame is instrumented - all important activity generates trace data.

re-frame-trace consumes this trace data and renders useful visualisations of the re-frame process. Currently, re-frame's tracing capabilities are in alpha and are subject to change at any time. We're testing the utility of the the trace by building an app on top.

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 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 make a PR to reagent to add proper hooks, once we know exactly what we need. The preload namespace also injects a div containing the devtools panel into the DOM.

Developing/Contributing

If you want to work on re-frame-trace, see DEVELOPERS.md.

Citations

• open by Bluetip Design from the Noun Project
• reload by Adnen Kadri from the Noun Project
• Camera by Christian Shannon from the Noun Project
• Delete by logan from the Noun Project
• Settings by arjuazka from the Noun Project
• Wrench by Aleksandr Vector from the Noun Project
• pause by Bhuvan from the Noun Project
• play by Bhuvan from the Noun Project
• Log Out by Arthur Shlain from the Noun Project