[whatwg] DOM Feature Mod: Add metering / parallelism & throttling options to AddEventListenerOptions

Jonathan Zuckerman j.zuckerman at gmail.com
Tue Nov 28 04:05:09 PST 2017

>From my own experience, only about half of the times I’ve required debounce
or throttle has been related to event handling, so if your proposal was
accepted I’d still need to include a library to satisfy the other scenarios.
On Tue, Nov 28, 2017 at 00:01 Sylon Zero <sylonzero at gmail.com> wrote:

> I think libraries having those functions emphasizes the point here, as
> that validates the existence and need for those patterns which then raises
> the requirement: should this be native to the browser?
> I believe the answer is yes, given how much work has already been put into
> standardizing the resource/computation model around the browser (web
> workers, local storage, etc) which is architecturally, IMHO, a related
> effort. Those capabilities come to life when there are smarter ways to
> utilize and route work to them through built-in features related to
> processing events/messages. In an effort to not create a science project
> out of some sort of top-down attack on this requirement, a simple
> middle-out approach with immediate results would be to extend the
> eventListener behavior that is prevalent in both browser and node.js
> scenarios.
> The case I am making first and foremost is that these recognizable
> patterns will be increasingly requisite (and not an after-thought, to be
> brought in via Underscore) in building web apps in the near term as web app
> complexity & use has increased dramatically with multiple cloud-scale
> offerings running in the SaaS space (think Netflix, LinkedIn, Facebook,
> Slack, etc) and more being built in various startups & emerging
> businesses. If the browser is to gain parity as an Application Platform
> allowing the development of web applications to rival native ones, then the
> ability to deal with volatile/durable messaging and events, storage and
> routing of work should be a core capability.
> *Broader implications:*
> If I may, let me add that I also think there is a growing confluence
> between the hybrid desktop app and browser-based SPAs (the Electron
> framework and its numerous successful projects like Atom, Slack, Visual
> Studio Code are great examples) and if the browser is to continue to evolve
> as a platform to encourage this trend (which is fabulous for the web
> community), then investments must be made to extend / normalize the browser
> standards in much the same way that the concept of a standardized
> Application Server helped standardize app architectures. This implies a
> future with registration of libraries/components (managed code), better
> local storage/caching options, improved integration with security contexts
> (per O/S), and likely much more. At least, I think it does :-).
> On Mon, Nov 27, 2017 at 6:48 PM, Jonathan Zuckerman <j.zuckerman at gmail.com
> > wrote:
>> You’re probably aware there are libraries that offer functionality of
>> this sort (debounce and throttle in underscore/lodash is the one I’m most
>> familiar with) and the web community seems content to add a small
>> dependency when such functionality is required. How would you convince
>> browser vendors to implement this?
>> On Mon, Nov 27, 2017 at 18:05 Sylon Zero <sylonzero at gmail.com> wrote:
>>> *Core Problem Statement* Processor functions that subscribe to events
>>> via a
>>> topic string may need to be prioritized for processing based on the topic
>>> itself. Conversely, certain events may be more numerous but should not
>>> limit the ability of the JS environment to respond and process other
>>> events, that may be more critical to either the User Experience (UX) or
>>> integrity of the system (e.g. events that trigger saving data to a
>>> back-end).
>>> *Background Information* As Browser/CommonJS environments bring paradigms
>>> like UI event handling and back-end event handling into the same problem
>>> space, it is useful to apply common patterns used in Message-based
>>> Publish-Subscribe environments with message brokers, which is what the JS
>>> execution context often behaves as. The use case here is to ensure that
>>> one
>>> kind of event (e.g. event listeners for a ‘mouseMove’ event) don’t
>>> saturate
>>> or delay execution of other events (e.g. ‘dataAvailableForAutosave’) due
>>> to
>>> massive differences in event volume or conversely, expensive operations
>>> that block the execution thread in question.
>>> *Proposed Solution* Add metering options to the addEventListener
>>> *Options* configuration
>>> object. These options control how the JS execution environment controls
>>> the
>>> throttling/firing of event handler instances in response to events that
>>> match the topic string of the subscription created by addEventListener.
>>> Proposed options:
>>>    - maxInstances [Number / Function] used to decide how many event
>>>    listeners can be invoked before throttling occurs. Throttling does
>>> not lose
>>>    events but simply queues them.
>>>    - throttlingQueueLength [Number] used to maintain an in-memory queue
>>> of
>>>    un-processed events per Topic string, after throttling kicks in.
>>>    - throttlingQueuePolicy [String] Values could be exception - throws an
>>>    exception when the queue length is exceeded, rolling - drops the
>>> oldest
>>>    events and pushes newer ones into the queue, expand- allow the queue
>>> to
>>>    expand to cover all events.
>>> *Additional Options* It might be even more useful if the options allowed
>>> targeting or creation of Web Workers (or Node child processes, depending
>>> on
>>> the execution context) based on the event handler configuration. This
>>> could
>>> potentially target CPU cores and/or O/S child processes / threads
>>> (depending on the O/S terminology for parallel execution).
>>> *Related Thread* The proposal identified in the link below (by Šime
>>> Vidas) could
>>> be part of this solution as it defines other metering options around
>>> debounce (which improves scale around event handling, which is in the
>>> same
>>> problem space) and handling throttling through frequency, which should be
>>> one of the alternatives in addition to my proposal above (as I believe
>>> they
>>> are orthogonal): https://discourse.wicg.io/t/add-event-throttlin
>>> g-and-debouncing-to-addeventlisteneroptions/2436/19
>>> Sai Prakash
>>> @SylonZero

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