213 lines
10 KiB
Markdown
213 lines
10 KiB
Markdown
# re-frame-trace
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`re-frame-trace` let's you instrument, and then inspect, the inner workings of a running `re-frame` application. It presents as a programmer's dashboard, delivering curated insight and illumination.
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### It Is Epoch Oriented
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`re-frame` applications are computationally regular. First an event happens,
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and then boom, boom, boom go a series of known computational steps (aka dominoes),
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in a known order. When this chain reaction completes,
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a `re-frame` app enters a quiescent state waiting for another
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event to kick off the next iteration of the same process.
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Each `re-frame` event and its consequent computation forms a bounded "epoch"
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which can be inspected, analysed and understood independently of other epochs. This
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tool is epoch-oriented - it shows you one at a time.
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And, yes, it has "time travel debugger" capabilities - you can go
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[backwards and forwards through epochs](https://condenaststore.com/featured/the-conga-line-of-past-selves-a-string-liana-finck.html) - but that's really not the most interesting or powerful aspect of what `re-frame-trace` delivers.
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### It Is About Trace Data
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As it runs, `re-frame` logs "trace" as data, and this provides an x-ray (MRI?) of your app's inner
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functioning. At its most basic level, `re-frame-trace` is a consumer, processor and presenter
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of trace data.
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### It Is About The Data Flow
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While re-frame is a functional framework, it is
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strongly defined by its "data oriented" design. `re-frame`
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"flows" data, in a loop, through the functions you provide.
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To understand what is happening in a `re-frame` app, you must understand
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what data is "happening".
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### It Is Always About The Data
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So, clearly, data is at the core of `re-frame-trace` for both of the reasons
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just outlined, but its importance is even more base and fundamental than that.
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Each time you put a `println` into your program, you are printing out what?
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And why? Invariably, it is data which fuels your debugging investigation,
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confirming your current hypothesis, or not.
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And when you write your unittests, you represent your expections as what? Correct
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data is the very definition of success.
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So, for debugging and understanding activities, more data, more easily is winning. Going back
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and adding a `println` shouldn't be necessary. All the data you need should already
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be captured, and it should be readily available in your REPL for further experimentation.
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### Data Brings Code To Life
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Perhaps you have seen LightTable in action?
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In the small, it is a delightfully productive debugging environment because it co-renders
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code and the data generated by running the code. The data provides a "paper trail" which
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brings the code to life, revealing its dynamics and enriching
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a programmer's understanding.
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`re-frame-trace` has a similar goal, although the method is different.
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### It Is A Data Dashboard
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Observing raw data trace is both interesting and valuable, but it isn't enough.
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First, we want to leverage this data for insights. And, second, there's often too much data - you
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can drown in the detail.
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So, `re-frame-trace` tries to be a "dashboard" which curates this
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"raw data" into "information" through various kinds of analysis
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and "roll ups". It should deliver insight "at a glance", while still allowing
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you to drill down into the detail.
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### Which Is Helpful How?
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Four ways:
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1. It helps you to learn `re-frame`. Simply looking at
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the "raw traces" provides insight into how it operates. Even experienced
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re-framians, er, like me, have learned a lot.
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2. It helps you to explore and learn an unfamiliar `re-frame` codebase.
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When I click, over here, on this "X" button, it shows me what event is `dispatch`-ed
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and in what namespace the associated event handler is registered. And,
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"oh look, that's interesting - four subscriptions recalculated". Etc.
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3. It helps you with debugging. You see an x-ray of your app's functioning.
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In particular, it will assist you to write and debug
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event handlers, which is useful because they hold most of the logic
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in your `re-frame` apps.
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4. It helps you to find performance problems and/or detect where there is
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unnecessary computation occurring.
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Point 3, is primary, of course. But Point 2 is almost as important because we all spend a
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lot of our time groking unfamiliar codebases. Being able to observe the inner
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workings of a running app is a great way to bring code to life, reveal key
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features, and build a cognative map of how the code is structured.
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### Temporary Warning
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> Some of the claims above are aspirational. `re-frame-trace` [remains a WIP](https://github.com/Day8/re-frame-trace/issues/118).
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## Of Sausage And Sizzle
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Internal discussion about a name meandered for a while. Initially, it was `re-frame-trace`, which is accurate, sure, but it is also 100% sausage because it talks about low level function, and not higher level benefit (sizzle, sizzle). Side stepping the issue, I wanted to call it `vox-datum` (voice of the data) but that was cruelly rejected, for reasons I don't care to remember. The pain. I mean, who the hell doesn't like a Latin name?? Philistines.
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Now, the tool's benifits are `-insight` and `-illumination`, but adding either made the name waaaay too long. Naming things - it really is a nightmare!
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Finally, `-10x` cheekily materialised, delivering 100 decibels of audacious sizzle, and consequently a challenge for us to live up to. A 10x programmer starts by having 10x more knowledge and insight - so go make that tool, smarty pants.
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## A 1000 words
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Slightly out of date, but indicative ...
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<img src="docs/images/re-frame-trace-demo.gif" height="500px">
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## Installation
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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](https://github.com/technomancy/leiningen/blob/stable/sample.project.clj).
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[](https://clojars.org/day8.re-frame/trace)
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- Update your re-frame dependency to at least `0.10.5` - `[re-frame "0.10.5"]`.
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- Add re-frame-trace as a dev dependency by placing `[day8.re-frame/trace "VERSION"]` within `:profiles :dev :dependencies`. For example:
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```cljs
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:profiles
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{:dev
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{:dependencies [[some-other-package "0.0.0"]
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[day8.re-frame/trace "0.0.0 (see version above)"]] }}
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```
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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"]`.
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- Locate the `:compiler` map under `:dev` and add:
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- `:closure-defines {"re_frame.trace.trace_enabled_QMARK_" true}`
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- `:preloads [day8.re-frame.trace.preload]`
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For example:
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```cljs
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{:builds
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[{:id "dev"
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:source-paths ["src" "dev"]
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:compiler {...
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:closure-defines {"re_frame.trace.trace_enabled_QMARK_" true}
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:preloads [day8.re-frame.trace.preload]
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}}]}
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```
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[cljs-devtools](https://github.com/binaryage/cljs-devtools) is not required to use re-frame-trace, but it is highly recommended.
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## Usage
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- **Make sure you have followed all of the installation instructions above.**
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- Start up your application.
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- Once it is loaded, focus the document window and press `ctrl-h` to slide open the trace panel and enable tracing.
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- When the panel is closed, tracing is disabled.
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## Use Cases
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### app-db
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* Inspect a portion of app-db's state with the path inspector, allowing you to focus on just the parts you care about.
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* Reset app-db to before an event was run to run it again, instead of resetting the whole application
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* Toggle app-db before and after states for running an event, to inspect UI changes.
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### Timing
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* Answer the question "Why is my app slow when it runs this event?"
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* See whether time is spent in processing an event, or rendering the changes
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## Troubleshooting
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* Try a `lein clean`
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* Make sure you have followed all the installation steps.
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### If re-frame-trace throws an exception on startup
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* Reset the settings to factory defaults in the settings panel
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* If you can't load the settings panel, run `day8.re_frame.trace.factory_reset_BANG_()` in the JavaScript console.
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* If neither of those work, remove all of the keys with the prefix `day8.re-frame.trace` from your browser's Local Storage.
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## How does it work?
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re-frame is instrumented - all important activity generates trace data.
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`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.
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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.
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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 [make a PR to reagent to add proper hooks](https://github.com/Day8/re-frame-trace/issues/115), once we know exactly what we need. The preload namespace also injects a div containing the devtools panel into the DOM.
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## Developing/Contributing
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If you want to work on re-frame-trace, see [DEVELOPERS.md](DEVELOPERS.md).
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## Citations
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* [open](https://thenounproject.com/search/?q=popout&i=334227) by Bluetip Design from the Noun Project
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* [reload](https://thenounproject.com/adnen.kadri/collection/arrows/?i=798299) by Adnen Kadri from the Noun Project
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* [Camera](https://thenounproject.com/search/?q=snapshot&i=200965) by Christian Shannon from the Noun Project
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* [Delete](https://thenounproject.com/term/delete/926276) by logan from the Noun Project
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* [Settings](https://thenounproject.com/search/?q=settings&i=1169241) by arjuazka from the Noun Project
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* [Wrench](https://thenounproject.com/icon/1013218/) by Aleksandr Vector from the Noun Project
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* [pause](https://thenounproject.com/icon/1376662/) by Bhuvan from the Noun Project
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* [play]() by Bhuvan from the Noun Project
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* [Log Out](https://thenounproject.com/icon/54484/) by Arthur Shlain from the Noun Project
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