Skip to content

re-frame.core

Dispatching Events

dispatch

(dispatch event)

Queue event for processing (handling).

event is a vector and the first element is typically a keyword which identifies the kind of event.

The event will be added to a FIFO processing queue, so event handling does not happen immediately. It will happen 'very soon' bit not now. And if the queue already contains events, they will be processed first.

Usage:

1
(dispatch [:order "pizza" {:supreme 2 :meatlovers 1 :veg 1}])

dispatch-sync

(dispatch-sync event)

Synchronously (immediately) process event. It does not queue the event for handling later as dispatch does.

event is a vector and the first element is typically a keyword which identifies the kind of event.

It is an error to use dispatch-sync within an event handler because you can't immediately process an new event when one is already part way through being processed.

Generally, avoid using this function, and instead, use dispatch. Only use it in the narrow set of cases where any delay in processing is a problem:

  1. the :on-change handler of a text field where we are expecting fast typing
  2. when initialising your app - see 'main' in examples/todomvc/src/core.cljs
  3. in a unit test where immediate, synchronous processing is useful

Usage:

1
(dispatch-sync [:sing :falsetto "piano accordion"])

Event Handlers

reg-event-db

(reg-event-db id handler)

(reg-event-db id interceptors handler)

Register the given event handler (function) for the given id. Optionally, provide an interceptors chain:

  • id is typically a namespaced keyword (but can be anything)
  • handler is a function: (db event) -> db
  • interceptors is a collection of interceptors. Will be flattened and nils removed.

Example Usage:

1
2
3
4
(reg-event-db
  :token
  (fn [db event]
    (assoc db :some-key (get event 2)))  ;; return updated db

Or perhaps:

1
2
3
4
5
6
7
(reg-event-db
  :namespaced/id           ;; <-- namespaced keywords are often used
  [one two three]          ;; <-- a seq of interceptors
  (fn [db [_ arg1 arg2]]   ;; <-- event vector is destructured
    (-> db
      (dissoc arg1)
      (update :key + arg2))))   ;; return updated db

reg-event-fx

(reg-event-fx id handler)

(reg-event-fx id interceptors handler)

Register the given event handler (function) for the given id. Optionally, provide an interceptors chain:

  • id is typically a namespaced keyword (but can be anything)
  • handler is a function: (coeffects-map event-vector) -> effects-map
  • interceptors is a collection of interceptors. Will be flattened and nils removed.

Example Usage:

1
2
3
4
(reg-event-fx
  :event-id
  (fn [cofx event]
    {:db (assoc (:db cofx) :some-key (get event 2))}))   ;; return a map of effects

Or perhaps:

1
2
3
4
5
6
(reg-event-fx
  :namespaced/id           ;; <-- namespaced keywords are often used
  [one two three]          ;; <-- a seq of interceptors
  (fn [{:keys [db] :as cofx} [_ arg1 arg2]] ;; destructure both arguments
    {:db       (assoc db :some-key arg1)          ;; return a map of effects
     :dispatch [:some-event arg2]}))

reg-event-ctx

(reg-event-ctx id handler)

(reg-event-ctx id interceptors handler)

Register the given event handler (function) for the given id. Optionally, provide an interceptors chain:

  • id is typically a namespaced keyword (but can be anything)
  • handler is a function: context-map -> context-map

You can explore what is provided in context here.

Example Usage:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
(reg-event-ctx
  :event-id
  (fn [{:keys [coeffects] :as context}]
    (let [initial  {:db     (:db coeffects)
                    :event  (:event coeffects)
                    :fx     []}
          result   (-> initial
                     function1
                     function2
                     function3)
          effects  (selectkeys result [:db :fx])]
       (assoc context :effects effects))))

clear-event

(clear-event)

(clear-event id)

Unregisters event handlers (presumably registered previously via the use of reg-event-db or reg-event-fx).

When called with no args, it will unregister all currently registered event handlers.

When given one arg, assumed to be the id of a previously registered event handler, it will unregister the associated handler. Will produce a warning to console if it finds no matching registration.

Subscriptions

reg-sub

(reg-sub query-id & args)

A call to reg-sub associates a query-id WITH two functions.

The two functions provide 'a mechanism' for creating a node in the Signal Graph. When a node of type query-id is needed, the two functions can be used to create it.

The three arguments are:

  • query-id - typically a namespaced keyword (later used in subscribe)
  • optionally, an input signals function which returns the input data flows required by this kind of node.
  • a computation function which computes the value (output) of the node (from the input data flows)

Later, during app execution, a call to (subscribe [:sub-id 3 :blue]), will trigger the need for a new :sub-id Signal Graph node (matching the query [:sub-id 3 :blue]). And, to create that node the two functions associated with :sub-id will be looked up and used.

Just to be clear: calling reg-sub does not immediately create a node. It only registers 'a mechanism' (the two functions) by which nodes can be created later, when a node is bought into existence by the use of subscribe in a View Function.

The computation function is expected to take two arguments:

  • input-values - the values which flow into this node (how is it wierd into the graph?)
  • query-vector - the vector given to subscribe

and it returns a computed value (which then becomes the output of the node)

When computation function is called, the 2nd query-vector argument will be that vector supplied to the subscribe. So, if the call was (subscribe [:sub-id 3 :blue]), then the query-vector supplied to the computaton function will be [:sub-id 3 :blue].

The argument(s) supplied to reg-sub between query-id and the computation-function can vary in 3 ways, but whatever is there defines the input signals part of the mechanism, specifying what input values "flow into" the computation function (as the 1st argument) when it is called.

So, reg-sub can be called in one of three ways, because there are three ways to define the input signals part. But note, the 2nd method, in which a signals function is explicitly supplied, is the most canonical and instructive. The other two are really just sugary variations.

First variation - no input signal function given:

1
2
3
(reg-sub
  :query-id
  a-computation-fn)   ;; has signature:  (fn [db query-vec]  ... ret-value)

In the absence of an explicit signals function, the node's input signal defaults to app-db and, as a result, the value within app-db (a map) is is given as the 1st argument when a-computation-fn is called.

Second variation - a signal function is explicitly supplied:

1
2
3
4
(reg-sub
  :query-id
  signal-fn     ;; <-- here
  computation-fn)

This is the most canonical and instructive of the three variations.

When a node is created from the template, the signal function will be called and it is expected to return the input signal(s) as either a singleton, if there is only one, or a sequence if there are many, or a map with the signals as the values.

The current values of the returned signals will be supplied as the 1st argument to the a-computation-fn when it is called - and subject to what this signal-fn returns, this value will be either a singleton, sequence or map of them (paralleling the structure returned by the signal function).

This example signal function returns a 2-vector of input signals.

1
2
3
(fn [query-vec dynamic-vec]
   [(subscribe [:a-sub])
    (subscribe [:b-sub])])

The associated computation function must be written to expect a 2-vector of values for its first argument:

1
2
(fn [[a b] query-vec]     ;; 1st argument is a seq of two values
  ....)

If, on the other hand, the signal function was simpler and returned a singleton, like this:

1

(fn [query-vec dynamic-vec] (subscribe [:a-sub])) ;; <-- returning a singleton

then the associated computation function must be written to expect a single value as the 1st argument:

1
2
(fn [a query-vec]       ;; 1st argument is a single value
   ...)

Further Note: variation #1 above, in which an input-fn was not supplied, like this:

1
2
3
(reg-sub
  :query-id
  a-computation-fn)   ;; has signature:  (fn [db query-vec]  ... ret-value)

is the equivalent of using this 2nd variation and explicitly suppling a signal-fn which returns app-db:

1
2
3
4
(reg-sub
  :query-id
  (fn [_ _]  re-frame/app-db)   ;; <--- explicit signal-fn
  a-computation-fn)             ;; has signature:  (fn [db query-vec]  ... ret-value)

Third variation - syntax Sugar

1
2
3
4
5
6
(reg-sub
  :a-b-sub
  :<- [:a-sub]
  :<- [:b-sub]
  (fn [[a b] query-vec]    ;; 1st argument is a seq of two values
    {:a a :b b}))

This 3rd variation is just syntactic sugar for the 2nd. Instead of providing an signals-fn you provide one or more pairs of :<- and a subscription vector.

If you supply only one pair a singleton will be supplied to the computation function, as if you had supplied a signal-fn returning only a single value:

1
2
3
4
5
(reg-sub
  :a-sub
  :<- [:a-sub]
  (fn [a query-vec]      ;; only one pair, so 1st argument is a single value
    ...))

For further understanding, read the tutorials, and look at the detailed comments in /examples/todomvc/src/subs.cljs.

See also: subscribe

subscribe

(subscribe query)

(subscribe query dynv)

Given a query vector, returns a Reagent reaction which will, over time, reactively deliver a stream of values. So, in FRP-ish terms, it returns a Signal.

To obtain the current value from the Signal, it must be dereferenced:

1
2
3
(let [signal (subscribe [:items])
      value  (deref signal)]     ;; could be written as @signal
  ...)

which is typically written tersely as simple:

1
2
(let [items  @(subscribe [:items])]
  ...)

query is a vector of at least one element. The first element is the query-id, typically a namespaced keyword. The rest of the vector's elements are optional, additional values which parameterise the query performed.

dynv is an optional 3rd argument, which is a vector of further input signals (atoms, reactions, etc), NOT values. This argument exists for historical reasons and is borderline deprecated these days.

Example Usage:

1
2
3
(subscribe [:items])
(subscribe [:items "blue" :small])
(subscribe [:items {:colour "blue"  :size :small}])

Note: for any given call to subscribe there must have been a previous call to reg-sub, registering the query handler (functions) associated with query-id.

Hint

When used in a view function BE SURE to deref the returned value. In fact, to avoid any mistakes, some prefer to define:

1
(def <sub  (comp deref re-frame.core/subscribe))

And then, within their views, they call (<sub [:items :small]) rather than using subscribe directly.

De-duplication

Two, or more, concurrent subscriptions for the same query will source reactive updates from the one executing handler.

See also: reg-sub

clear-sub

(clear-sub)

(clear-sub query-id)

Unregisters subscription handlers (presumably registered previously via the use of reg-sub).

When called with no args, it will unregister all currently registered subscription handlers.

When given one arg, assumed to be the id of a previously registered subscription handler, it will unregister the associated handler. Will produce a warning to console if it finds no matching registration.

NOTE: Depending on the usecase, it may be necessary to call clear-subscription-cache! afterwards

reg-sub-raw

(reg-sub-raw query-id handler-fn)

This is a low level, advanced function. You should probably be using reg-sub instead.

Some explanation is available in the docs at http://day8.github.io/re-frame/flow-mechanics/

clear-subscription-cache!

(clear-subscription-cache!)

Removes all subscriptions from the cache.

This function can be used at development time or test time. Useful when hot realoding namespaces containing subscription handlers. Also call it after a React/render exception, because React components won't have been cleaned up properly. And this, in turn, means the subscriptions within those components won't have been cleaned up correctly. So this forces the issue.

Effect Handlers

reg-fx

(reg-fx id handler)

Register the given effect handler for the given id:

  • id is keyword, often namespaced.
  • handler is a side-effecting function which takes a single argument and whose return value is ignored.

To use, first, associate :effect2 with a handler:

1
2
3
4
(reg-fx
   :effect2
   (fn [value]
      ... do something side-effect-y))

Then, later, if an event handler were to return this effects map:

1
{:effect2  [1 2]}

then the handler fn we registered previously, using reg-fx, will be called with an argument of [1 2].

clear-fx

(clear-fx)

(clear-fx id)

Unregisters effect handlers (presumably registered previously via the use of reg-fx).

When called with no args, it will unregister all currently registered effect handlers.

When given one arg, assumed to be the id of a previously registered effect handler, it will unregister the associated handler. Will produce a warning to console if it finds no matching registration.

Coeffects

reg-cofx

(reg-cofx id handler)

Register the given coeffect handler for the given id, for later use within inject-cofx:

  • id is keyword, often namespaced.
  • handler is a function which takes either one or two arguements, the first of which is always coeffects and which returns an updated coeffects.

See also: inject-cofx

inject-cofx

(inject-cofx id)

(inject-cofx id value)

Given an id, and an optional, arbitrary value, returns an interceptor whose :before adds to the :coeffects (map) by calling a pre-registered 'coeffect handler' identified by the id.

The previous association of a coeffect handler with an id will have happened via a call to re-frame.core/reg-cofx - generally on program startup.

Within the created interceptor, this 'looked up' coeffect handler will be called (within the :before) with two arguments:

  • the current value of :coeffects
  • optionally, the originally supplied arbitrary value

This coeffect handler is expected to modify and return its first, coeffects argument.

Example of inject-cofx and reg-cofx working together

First - Early in app startup, you register a coeffect handler for :datetime:

1
2
3
4
5
(re-frame.core/reg-cofx
  :datetime                        ;; usage  (inject-cofx :datetime)
  (fn coeffect-handler
    [coeffect]
    (assoc coeffect :now (js/Date.))))   ;; modify and return first arg

Second - Later, add an interceptor to an -fx event handler, using inject-cofx:

1
2
3
4
5
6
7
(re-frame.core/reg-event-fx            ;; when registering an event handler
  :event-id
  [ ... (inject-cofx :datetime) ... ]  ;; <-- create an injecting interceptor
  (fn event-handler
    [coeffect event]
      ;;... in here can access (:now coeffect) to obtain current datetime ...
    )))

Background

coeffects are the input resources required by an event handler to perform its job. The two most obvious ones are db and event. But sometimes an event handler might need other resources.

Perhaps an event handler needs a random number or a GUID or the current datetime. Perhaps it needs access to a DataScript database connection.

If an event handler directly accesses these resources, it stops being pure and, consequently, it becomes harder to test, etc. So we don't want that.

Instead, the interceptor created by this function is a way to 'inject' 'necessary resources' into the :coeffects (map) subsequently given to the event handler at call time.

See also reg-cofx

clear-cofx

(clear-cofx)

(clear-cofx id)

Unregisters coeffect handlers (presumably registered previously via the use of reg-cofx).

When called with no args, it will unregister all currently registered coeffect handlers.

When given one arg, assumed to be the id of a previously registered coeffect handler, it will unregister the associated handler. Will produce a warning to console if it finds no matching registration.

Interceptors

debug

An interceptor which logs/instruments an event handler's actions to js/console.debug. See examples/todomvc/src/events.cljs for use.

Output includes:

  1. the event vector
  2. a clojure.data/diff of db, before vs after, which shows the changes caused by the event handler. To understand the output, you should understand: https://clojuredocs.org/clojure.data/diff.

You'd typically include this interceptor after (to the right of) any path interceptor.

Warning: calling clojure.data/diff on large, complex data structures can be slow. So, you won't want this interceptor present in production code. So, you should condition it out like this:

1
2
3
4
5
(re-frame.core/reg-event-db
  :evt-id
  [(when ^boolean goog.DEBUG re-frame.core/debug)]  ;; <-- conditional
  (fn [db v]
     ...))

To make this code fragment work, you'll also have to set goog.DEBUG to false in your production builds. For an example, look in project.clj of /examples/todomvc.

path

(path & args)

Returns an interceptor which acts somewhat like clojure.core/update-in, in the sense that the event handler is given a specific part of app-db to change, not all of app-db.

The interceptor has both a :before and :after functions. The :before replaces the :db key within coeffects with a sub-path within app-db. The :after reverses the process, and it grafts the handler's return value back into db, at the right path.

Examples:

1
2
3
4
(path :some :path)
(path [:some :path])
(path [:some :path] :to :here)
(path [:some :path] [:to] :here)

Example Use:

1
2
3
4
5
(reg-event-db
  :event-id
  (path [:a :b])  ;; <-- used here, in interceptor chain
  (fn [b v]       ;; 1st arg is not db. Is the value from path [:a :b] within db
    ... new-b))   ;; returns a new value for that path (not the entire db)

Notes:

  1. path may appear more than once in an interceptor chain. Progressive narrowing.
  2. if :effects contains no :db effect, can't graft a value back in.

enrich

(enrich f)

Returns an Interceptor which will run the given function f in the :after position.

f is called with two arguments: db and v, and is expected to return a modified db.

Unlike the after interceptor which is only about side effects, enrich expects f to process and alter the given db coeffect in some useful way, contributing to the derived data, flowing vibe.

Example Use:

Imagine that todomvc needed to do duplicate detection - if any two todos had the same text, then highlight their background, and report them via a warning at the bottom of the panel.

Almost any user action (edit text, add new todo, remove a todo) requires a complete reassessment of duplication errors and warnings. Eg: that edit just made might have introduced a new duplicate, or removed one. Same with any todo removal. So we need to re-calculate warnings after any CRUD events associated with the todos list.

Unless we are careful, we might end up coding subtly different checks for each kind of CRUD operation. The duplicates check made after 'delete todo' event might be subtly different to that done after an editing operation. Nice and efficient, but fiddly. A bug generator approach.

So, instead, we create an f which recalculates ALL warnings from scratch every time there is ANY change. It will inspect all the todos, and reset ALL FLAGS every time (overwriting what was there previously) and fully recalculate the list of duplicates (displayed at the bottom?).

https://twitter.com/nathanmarz/status/879722740776939520

By applying f in an :enrich interceptor, after every CRUD event, we keep the handlers simple and yet we ensure this important step (of getting warnings right) is not missed on any change.

We can test f easily - it is a pure function - independently of any CRUD operation.

This brings huge simplicity at the expense of some re-computation each time. This may be a very satisfactory trade-off in many cases.

unwrap

New in v1.2.0

An interceptor which decreases the amount of destructuring necessary in an event handler where the event is structured as a 2-vector of [event-id payload-map].

It promotes the payload-map part to be the event ultimately given to the event handler. Should you want the full original event, it can be found in coeffects under the key :original-event.

If a dispatch looked like this:

1
 (dispatch [:event-id {:x 1 :y 2 :z 3}])

Your event handlers can look like this:

1
2
3
4
5
 (reg-event-fx
   :event-id
   [... unwrap ...]                    ;; <-- added to the interceptors
   (fn [{:keys [db]} {:keys [x y z]}]  ;; <-- instead of [_ {:keys [x y z]}]
     ...)

trim-v

An interceptor which removes the first element of the event vector, before it is supplied to the event handler, allowing you to write more aesthetically pleasing event handlers. No leading underscore on the event-v!

Should you want the full original event, it can be found in coeffects under the key :original-event.

Your event handlers will look like this:

1
2
3
4
5
(reg-event-db
  :event-id
  [... trim-v ...]    ;; <-- added to the interceptors
  (fn [db [x y z]]    ;; <-- instead of [_ x y z]
    ...)

after

(after f)

Returns an interceptor which runs the given function f in the :after position, presumably for side effects.

f is called with two arguments: the :effects value for :db (or the :coeffect value of :db if no :db effect is returned) and the event. Its return value is ignored, so f can only side-effect.

An example of use can be seen in the re-frame github repo in /examples/todomvc/events.cljs:

  • f runs schema validation (reporting any errors found).
  • f writes to localstorage.

on-changes

(on-changes f out-path & in-paths)

Returns an interceptor which will observe N paths within db, and if any of them test not identical? to their previous value (as a result of a event handler being run), then it will run f to compute a new value, which is then assoc-ed into the given out-path within db.

Example Usage:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
(defn my-f
  [a-val b-val]
  ... some computation on a and b in here)

;; use it
(def my-interceptor (on-changes my-f [:c] [:a] [:b]))

(reg-event-db
  :event-id
  [... my-interceptor ...]  ;; <-- ultimately used here
  (fn [db v]
     ...))

If you put this Interceptor on handlers which might change paths :a or :b, it will:

  • call f each time the value at path [:a] or [:b] changes
  • call f with the values extracted from [:a] [:b]
  • assoc the return value from f into the path [:c]

Global Interceptors

reg-global-interceptor

(reg-global-interceptor interceptor)

Registers the given interceptor as a global interceptor. Global interceptors are included in the processing chain of every event.

When you register an event handler, you have the option of supplying an interceptor chain. Any global interceptors you register are effectively prepending to this chain.

Global interceptors are run in the order that they are registered.

clear-global-interceptor

(clear-global-interceptor)

(clear-global-interceptor id)

Unregisters global interceptors (presumably registered previously via the use of reg-global-interceptor).

When called with no args, it will unregister all currently registered global interceptors.

When given one arg, assumed to be the id of a previously registered global interceptors, it will unregister the associated interceptor. Will produce a warning to console if it finds no matching registration.

Writing Interceptors

->interceptor

(->interceptor & {:as m, :keys [id before after]})

A utility function for creating interceptors.

Accepts three optional, named arguments:

  • :id - an id for the interceptor (decorative only)
  • :before - the interceptor's before function
  • :after - the interceptor's after function

Example use:

1
2
3
4
5
6
7
(def my-interceptor
  (->interceptor
   :id     :my-interceptor
   :before (fn [context]
             ... modifies and returns `context`)
   :after  (fn [context]
             ... modifies and returns `context`)))

Notes:

  • :before functions modify and return their context argument. Sometimes they only side effect, in which case, they'll perform the side effect and return context unchanged.
  • :before functions often modify the :coeffects map within context and, if they do, then they should use the utility functions get-coeffect and assoc-coeffect.
  • :after functions modify and return their context argument. Sometimes they only side effect, in which case, they'll perform the side effect and return context unchanged.
  • :after functions often modify the :effects map within context and, if they do, then they should use the utility functions get-effect and assoc-effect

get-coeffect

(get-coeffect context)

(get-coeffect context key)

(get-coeffect context key not-found)

A utility function, typically used when writing an interceptor's :before function.

When called with one argument, it returns the :coeffects map from with that context.

When called with two or three arguments, behaves like clojure.core/get and returns the value mapped to key in the :coeffects map within context, not-found or nil if key is not present.

assoc-coeffect

(assoc-coeffect context key value)

A utility function, typically used when writing an interceptor's :before function.

Adds or updates a key/value pair in the :coeffects map within context.

get-effect

(get-effect context)

(get-effect context key)

(get-effect context key not-found)

A utility function, used when writing interceptors, typically within an :after function.

When called with one argument, returns the :effects map from the context.

When called with two or three arguments, behaves like clojure.core/get and returns the value mapped to key in the effects map, not-found or nil if key is not present.

assoc-effect

(assoc-effect context key value)

A utility function, typically used when writing an interceptor's :after function.

Adds or updates a key/value pair in the :effects map within context.

enqueue

(enqueue context interceptors)

A utility function, used when writing an interceptor's :before function.

Adds the given collection of interceptors to those already in context's execution :queue. It returns the updated context.

So, it provides a way for one Interceptor to add more interceptors to the currently executing interceptor chain.

Logging

set-loggers!

(set-loggers! new-loggers)

re-frame outputs warnings and errors via the API function console which, by default, delegates to js/console's default implementation for log, error, warn, debug, group and groupEnd. But, using this function, you can override that behaviour with your own functions.

The argument new-loggers should be a map containing a subset of they keys for the standard loggers, namely :log :error :warn :debug :group or :groupEnd.

Example Usage:

1
2
3
4
5
6
(defn my-logger      ;; my alternative logging function
  [& args]
  (post-it-somewhere (apply str args)))

;; now install my alternative loggers
(re-frame.core/set-loggers!  {:warn my-logger :log my-logger})

console

(console level & args)

A utility logging function which is used internally within re-frame to produce warnings and other output. It can also be used by libraries which extend re-frame, such as effect handlers.

By default, it will output the given args to js/console at the given log level. However, an application using re-frame can redirect console output via set-loggers!.

level can be one of :log, :error, :warn, :debug, :group or :groupEnd.

Example usage:

1
2
(console :error "Sure enough it happened:" a-var "and" another)
(console :warn "Possible breach of containment wall at:" dt)

Miscellaneous

make-restore-fn

(make-restore-fn)

This is a utility function, typically used in testing.

It checkpoints the current state of re-frame and returns a function which, when later called, will restore re-frame to the checkpointed state.

The checkpoint includes app-db, all registered handlers and all subscriptions.

purge-event-queue

(purge-event-queue)

Removes all events currently queued for processing

add-post-event-callback

(add-post-event-callback f)

(add-post-event-callback id f)

Registers the given function f to be called after each event is processed.

f will be called with two arguments:

  • event: a vector. The event just processed.
  • queue: a PersistentQueue, possibly empty, of events yet to be processed.

This facility is useful in advanced cases like:

  • you are implementing a complex bootstrap pipeline
  • you want to create your own handling infrastructure, with perhaps multiple handlers for the one event, etc. Hook in here.
  • libraries providing 'isomorphic javascript' rendering on Nodejs or Nashorn.

id is typically a keyword. If it supplied when an f is added, it can be subsequently be used to identify it for removal. See remove-post-event-callback.

remove-post-event-callback

(remove-post-event-callback id)

Unregisters a post event callback function, identified by id.

Such a function must have been previously registered via add-post-event-callback

Deprecated

register-handler

(register-handler & args)

Deprecated. Use reg-event-db instead.

register-sub

(register-sub & args)

Deprecated. Use reg-sub-raw instead.