re-frame/CHANGES.md

0.8.0 (2016.07.XX)

Staying on the leading edge of new buzzwords is obviously critical for any framework. Angluar's terrifying faceplant is a sobering reminder to us all.
With this release, re-frame's already impressive buzzword muscles bulge further with new walnuts like "effects", "coeffects", and "de-duplicated signal graph". I know, right?

Some may even find the new features useful.

Headline:

• re-frame subscriptions are now de-duplicated. As a result, many Signal graphs will be more efficient. The new behaviour better matches programmer intuitions about what "should" happen.

  Explanation

  Each subscription causes a handler to execute, producing a reactive stream of updates. Two calls to (subscribe [:some :query]) results in two copies of the same subscription handler running, each delivering a stream of updates. Now, if these two subscriptions were running at the same time, this would be inefficient. Both handlers would be doing the same computations and delivering the same stream of updates. Unnecessary, duplicate work.

  Starting with this version, this sort of duplication has been eliminated. Two, or more, concurrent subscriptions for the same query will now source reactive updates from the one executing handler.

  So, how do we know if two subscriptions are "the same"? Answer: two subscriptions are the same if their query vectors test = to each other.

  So, these two subscriptions are not "the same": [:some-event 42] [:some-event "blah"]. Even though they involve the same event id, :some-event, the query vectors do not test =.

• added a new subscription handler registration function called re-frame.core/def-sub. It is an alternative to re-frame.core/register-sub (now renamed to re-frame.core/def-sub-raw). def-sub is significantly easier to use and understand, while often also being more performant. The design has really fallen out nicely and we're delighted with it.

  With def-sub, you no longer need to use reaction explicitly. Subscription handlers are now pure which makes them easier to understand and test etc. Plus, as you'll see in the docs, there is some gratuitous syntactic sugar.

  The todomvc example is a tutorial on the subject:
  https://github.com/Day8/re-frame/blob/master/examples/todomvc/src/todomvc/subs.cljs

• The API for the undo/redo features has been put into re-frame.core.
  Detailed documentation is now available: https://github.com/Day8/re-frame/wiki/Undo-&-Redo
  While undo and redo has been a part of re-frame from the beginning, the feature has been hidden and not documented, so it is nice to see it given proper API status. Plus, this release has a couple of enhancements over that which previously existed previously.

• there's now two kinds of event handlers: pure and effectful. XXX
  For description see: https://github.com/Day8/re-frame/wiki/Effectful-Event-Handlers

Breaking:

• requires Reagent >= v0.6.0

• requires ClojureScript >= 1.9.0, because the specs library is used. XXX not true yet. 1.8.0 is fine.

• re-frame.core/register-handler has been renamed re-frame.core/def-event. (There's now two kinds of event-handlers, pure and effectful. Event handlers of the 2nd, new kind should be registered via the new function re-frame.core/def-event-fx)

• re-frame.core/register-sub has been renamed re-frame.core/def-sub-raw. This is to indicate that this kind of registration is now considered the low level, close to the metal way to create subscriptions handlers. This release introduced def-sub which becomes the preferred way to register subscription handlers.

• By default, re-frame uses js/console functions like error and warn when logging, but you can
  supply alternative functions using re-frame.core/set-loggers!.

  With this release, any alternatives you supply will be called with different parameters. Previously loggers were called with a single str parameter but now they are expected to act like console.log itself and take variadic, non string params. Sorry to break things, but we are trying to maximise use of cljs-devtools and information is lost when strings are output, instead of actual data.

  To transition, you'll need to tweak like this:

   ;; your old log function might have looked like this. Single string parameter.
  (defn my-logger [s]  (do-something-with s))    
  
  ;; your new version will have variadic params, and turn them into a string
  (defn my-logger [& args] (do-something-with (apply str args))
  

  Of course, you need only worry about this if you are using re-frame.core/set-loggers! to hook in your own loggers. Otherwise, you have nothing to do.

Improvements

• XXX (full-debug!)

• XXX middleware for spec checking of event vectors

• XXX todomvc changed to use spec, instead of Schema

• Bug fix: post-event-callbacks were not called when dispatch-sync was called.

• added new API re-frame.core/remove-post-event-callback. See doc string.

• when an event-handler makes no change to app-db, the debug middleware now logs a single line saying so, rather than a "group". Makes it slightly easier to grok the absence of change.

0.7.0 (2016-03-14)

Breaking:

• removed middleware log-ex. It is no longer needed because browsers now correctly report the throw site of re-thown exceptions. In the unlikely event that you absolutely still need it, the source for log-ex is still in middleware.cljs, commented out. Just transfer it to your project.

• debug middleware now produces slightly different output (to console). So no code will need to change, just your expectations of what you see in console. Previously all console output from an event handler was put into the one console group, which could lead to exceptions being hidden (down in a closed group).

Improvements:

• added one tick of extra pause when events have :flush=dom metadata. Previously, there were odd times when the pause wasn't long enough to ensure redraws.
• now compatible with Reagent 0.6.0 (but this not fully tested) while remaining backwards compatible with Reagent v0.5.1
• #138 Switch to using CircleCI and automated testing with Karma

Fixed:

• #149 Undo now discards oldest undo states, not the newest ones.

0.6.0 (2015-12-09)

New API:

• #118 - Add add-post-event-callback to the API. @pupeno is developing preprender which looks pretty neat. Support this effort by adding a way for preprender to hook event processing.

• on-changes middleware now official. No longer experimental.

Improvements:

• #134 My thanks to @scgilardi for a nice simplification of the routing state machine. Again!
• #133 Improve Readme formatting

0.5.0 (2015-11-5)

New Features:

• #108 - Add dynamic subscriptions. Docs to follow, and your cheque is in the mail.

Improvements:

• fixed problem with log grouping

• removed -------New Event------- log msg

• made groups collapsed by default

• #104 - Updated to the latest TodoMVC CSS

• Reimplemented the router loop. Removed use of core.async. Replaced with hand rolled scheduling. See 420e42a As a result:

  • there is less of a pause between a dispatch and the associated event handler being run. (<1ms vs 5ms??)
  • groups of events queued up will be handled in a batch, one after the other, without yielding to the browser (previously re-frame yielded to the browser before every single event).

  This fixes issues like #39 and #121

  I doubt this will affect normal apps. But it could affect games which depend on existing timings. Maybe. It could affect apps which dispatch large volumes of events (telemetry?) very quickly. Maybe.

v0.4.1 (2015-05-29)

Improvements:

• fix #65 - Detect mistaken use of middleware factories
• examples/ now work with figwheel

v0.4.0 (2015-05-04)

Headline:

• Exceptions in event handlers no longer break the router loop. Previously, any exception in an event handler broke the app permanently. This change will:
  • improve the debugging experience with figwheel
  • mean apps, in production, stand a chance of reporting UHE to the user, and can perhaps even recover to a sane state.
• #53 Fix Logging And Error Reporting You can now provide your own logging fucntions. Further explanation here.

Deprecated:

• log-ex middleware is no longer needed. Simply remove its use. Sometime in the last couple of months, changes to the CLJS runtime meant that useful exceptions could escape go-loops, and good stack traces appear (at least in Chrome).

New Features:

• #52 Add a way to purge redos (dispatch [:purge-redos]) When trying to recover from an UHE, do an undo to get back to the last sane state, and then use this new feature to purge the just-generated-redo.
• #43 Add ability to clear handlers (event and subs) via two new API functions:
  • re-frame.core/clear-sub-handlers!
  • re-frame.core/clear-event-handlers! Useful for those using the ClojureScript fork of Component.

Experimental:

• #50 Add "reaction-like" middleware called on-changes.

Other:

• improve some comments in todomvc example

v0.3.2 (2015-04-21)

Improvements:

• Fix #42 - Put in checks for dispatch-sync
• Fix #49 - add table of content and link to wiki for middleware
• Fix #46 - Minor typos fixed

v0.3.1 (2015-04-18)

Various small improvements and bug fixes:

• log-ex middleware added to core api (it was a mistake that it was missing)
• modest improves to simple example. Better comments, layout, etc.
• the anonymous functions in standard middleware now have meaningful names, which makes stack traces easier to understand.
• #24 - Fix missing paren in README
• #31 - Fix list formatting in README
• #32 - fix a broken wiki link
• #30 - Fix up the enrich docstring

v0.3.0 (2015-04-15)

Headline

• the middleware after and enrich now call the supplied function f with both db and v (previously just db). Because javascript is so forgiving about function arity, this change is backwards compatible.
• new event handler middleware log-ex for correctly printing handler stacktraces. See explanation.
• ongoing improvements to the docs in Wiki

Other

• move to reagent v0.5.0
• fix undo bug which could result in incorrect explanations.
• improve todomvc's use of localstorage
• experimental work with slimmer.js for testing
• correct README wiki links
• license.txt was incorrectly named previously

v0.2.0 (2015-03-06)

Breaking

Renames:

• register-pure-handler renamed to register-handler (and existing low level register-handler becomes register-handler-base but is not a part of the API).
• remove apply-event middleware and replace with similar trim-v
• rename register-subs to register-sub (avoid confusion over possible plurals)
• rename set-max-undos to set-max-undos!

Changes:

• undoable middleware is now a factory. Where before you used this undoable, you must now use this (undoable "some explanation"). See further below.

Headline

• exceptions in handler now reported more sanely via console.error. (core.async really messes with a good stack)
• example todomvc available in examples folder.
• Wiki documentation is now more substantial.
• introduce new handler middleware: debug, enrich and after

Other:

• exceptions in a go loop are a special type of hell. Improve the reporting of exceptions happening in event handlers.
• allow Middleware to be registered as a vector. data > functions > macros
• fix two bugs in undo implementation
• name licence file correctly, thanks to @smith
• fix typo in readme, thanks to @btheado
• Readme now admits to 200 lines of code, not 100.
• dispatch now explicitly returns nil
• travis integration (not that we have any tests currently)

Details On Undo Changes

The undo/redo feature built into re-frame is now more functional (at the cost of a breaking change).

There is now an explanation associated with each undo state describing modification. This allows an app to inform the user what actions they will be undoing or redoing.

Previously undoable was simply middleware, but it is now a middleware factory.

Essentially, that means you can't use it "plain" anymore, and instead you must call it, like this (undoable "Some explanation")

The explanation provided to undoable must be either a string (static explanation) or a function (db event) -> string, allowing you to customize the undo message based on details of the event.