5 ms·

Debouncing refers to cleaning up the signal from an opening and closing switch contact so that the cleaned signal matches the intended semantics of the switch a

Debouncing refers to cleaning up the signal from an opening and closing switch contact so that the cleaned signal matches the intended semantics of the switch action (e.g. one simple press of a button, not fifty pulses). The analogy here is poor; reducing thrashing in those obnoxious search completion interfaces isn't like debouncing. Sure, if we ignore everything about it that is not like debouncing, and we still have something left after that, then whatever is left is like debouncing. One important difference is that if you have unlimited amounts of low latency and processing power, you can do a full search for each keystroke, filter it down to half a dozen results and display the completions. In other words, the more power you have, the less important it is to do any "debouncing". Switch debouncing is not like this. The faster is your processor at sampling the switch, the more bounces it sees and consequently the more crap it has to clean up. Debouncing certainly does not go away with a faster microcontroller.

maxbond 1y ago
It's the term used in frontend dev. It is actually a little worse than you're imagining, because we're not sampling, we're receiving callbacks (so more analogous to interrupts than sampling in a loop). Eg the oninput callback. I've used it for implementing auto save without making a localStorage call on every key press, for example. I think it makes sense if you view it from a control theory perspective rather than an embedded perspective. The mechanics of the UI (be that a physical button or text input) create a flaggy signal. Naively updating the UI on that signal would create jank. So we apply some hysteresis to obtain a clean signal. In the day way that acting 50 times on a single button press is incorrect behavior, saving (or searching or what have you) 50 times from typing a single sentence isn't correct (or at least undesired). The example of 10ms is way too low though, anything less than 250ms seems needlessly aggressive to me. 250ms is still going to feel very snappy. I think if you're typing at 40-50wpm you'll probably have an interval of 100-150ms between characters, so 10ms is hardly debouncing anything.
- Findecanor 1y ago
  An office keyboard's own debouncing could delay a key press 30 ms, and then the OS, software and graphics/monitor hardware would delay it just as much before the user could see the character on screen. So, indeed, 10 ms is much too low.
  - maxbond 1y ago
    Perhaps the people at MDN are 10x typists, with competition-grade gaming keyboards.
  - mindslight 1y ago
    No, correct debouncing of a hardware button should not add any delay to a single press. It's not wait-then-act, but rather act-then-wait-to-act-again. You're probably thinking of a polling interval (often exacerbated by having key switches wired in a matrix rather than one per pin).
    - maxbond 1y ago
      They describe that approach in another comment [1], so I take it to be a descriptive statement about low end keyboards. Perhaps the engineers designing these keyboards view 30ms as an acceptable latency to prevent spurious key presses. [1] https://news.ycombinator.com/item?id=44822183 https://news.ycombinator.com/item?id=44822183
    - kazinator 1y ago
      The bouncing behavior itself adds delay. If it takes 30 ms for the switch to settle to a state where it is considered closed according to the debouncing algorithm's parameters, then that's what it is. The algorithm might be "sample every millisecond, until 9 out of 10 samples show "closed". That imposes a minimum delay of 10 ms, and the maximum is whatever it takes for that criterion to be reached.
      - mindslight 1y ago
        That's a low pass filter. And I suppose in the type of highly-resilient slow changing signals like OP mentioned in a different comment, it makes sense to do that and even to refer to it as "debouncing". But for general consumer electronic devices with basic local buttons, the standard algorithm is something more like act on the first close, then ignore the next 10 samples. When there is no other reason for a switch to read as closed, the first close means the button has definitely been pushed. The point of debouncing is to avoid seeing the open-close-open-close oscillation afterwards (contacts settling) as their own release-press combos.
- zeta0134 1y ago
  Additionally, regardless of naming, debouncing is an accessibility feature for a surprisingly large portion of the population. Many users who grew up with double-click continue to attempt to provide this input on web forms, because it mostly works. Many more with motor control issues may struggle to issue just a single click reliably, especially on a touchscreen.
  - gibsonsmog 1y ago
    Holy moly, for years I've had in the back of my head this thought about why, earlier in my career, I'd see random doubly submitted form submissions on certain projects. Same form code and processing as other sites, legitimate submissions too. Eventually we added more spam filtering and restrictions unrelated to these legitimate ones, but it was probably the double-click users causing those errant submissions. I'd never even have thought of those users. Fascinating
    - Sharlin 1y ago
      Yes, it's something pretty much all UI frameworks end up implementing. The easiest way to do it is to simply disable the button at first click until the request is complete. This, of course, also prevents double submissions in cases the user doesn't get enough feedback and clicks again to make sure something actually happened.
      - deleted 1y ago
        [deleted]
    - kazinator 1y ago
      Users of GUI operating systems had been trained to double-click on icons representing applications or files in order to launch them. If you make a web UI in which a button is styled via an icon image (or otherwise) to look like a launchable application or file, those users will double click on it. If you make it look like a button, they won't; they were certainly not trained to double-click on [OK] or [Cancel] in an OK/Cancel dialog box, for instance! Double clicking to launch an action on a file makes sense because you need single click for selecting it. There are things you can do with it other than launch, like dragging it to another location. T;DR: don't make buttons look like elements that can be selected and dragged somewhere? -- Another reason: I've sometimes multiply clicked on some button-like thing in a web UI because in spite of working fine, it made no indication that had received the click! It was styled to look like a button in the unclicked state ... and that one image was all it had. To detect that the action launched you have to look for clues in the browser status areas showing that something is being loaded. Those are often made unobtrusive these days. Gone are the days of Netscape's spinning planet. When the user sees that a button doesn't change state upon being clicked, yet the normal cursor is seen (pointer, not hourglass or spinning thing or whatever) they assume that the application has become unresponsive due to a bug or performance problem, or that somehow the click event was dropped; maybe their button is physically not working or whatever.
- account42 1y ago
  > 250ms is still going to feel very snappy WTF no it won't.
  - schwartzworld 1y ago
    For the kind of behaviors they are describing it would. An extra 250ms waiting for an app to load is a lot, but for something like the described autosave behavior, waiting for a 250ms pause in typing before autosaving or making a fetch call is pretty snappy.
  - maxbond 1y ago
    What value would you recommend?
- deleted 1y ago
  [deleted]
- ndriscoll 1y ago
  Why would e.g. saving after each keypress be janky from the UI perspective? These days disks can complete a write in 20 us. If you're typing at 0.1 seconds/character, you're going 5,000 times slower than the computer is capable of. If you have a 60 Hz monitor, it can block saving your work every frame and still be 99.9% idle. Even if you're making network requests each time, if the request finishes in 20 ms, you're still done 80 ms before the user presses the next button.
  - schwartzworld 1y ago
    Local storage is a poor example because it updates in the background and wouldn’t necessarily change your UI much. But if a design calls for a search to be made while a user types that would get janky fast. React in particular is data driven so in the above example, if you make the api call on each keypress, and save it into state or whatever, the UI will update automatically. I can type 70 words per minute. Nobody wants the search results to update that fast. (Should we be building searches that work this way? Often you have no choice.) A slow network + a short search string + a not top of the line device like a cheap phone means a really janky experience. And even if it’s not janky, its a waste of your users bandwidth (not everybody has unlimited) and an unnecessary drain on your server resources. Even though we say “update as the user types” people type in bursts. There’s no reason not to debounce it, and if you can make the debounce function composable, you can reuse it all over the place. It’s a courtesy to the users and a good practice.
    - maxbond 1y ago
      Introducing auto save into the discussion may have been confusing, you're both right that that wouldn't generally cause jank, debouncing an auto save is more about not using resources unnecessarily and may help provide a better edit history depending on how you've written the application.
    - ndriscoll 1y ago
      I type around 90-100 wpm and I appreciate that clementine player for example doesn't seem to have any delay except apparently when querying radio stations (which is described as "to be polite"). When searching your own library, it updates immediately (I'd be very surprised if the query weren't faster than my monitor refresh). My only perception is that it's fast. I don't know why anyone would see it as janky. So it seems to me that it's entirely about not wasting resources/to be polite. In the limit where you have a computer that can do its work faster than your display refreshes, letting it do so seems to clearly make everything feel snappier. No one's typing quickly on a phone anyway and most people probably do a word at a time, and that word will come in slower than your denounce, so again there is no point in delaying it. One thing another user pointed out is that your search does need to be stable. An exact substring match shouldn't randomly get bumped down as you type more. A separate issue you might encounter for slow queries is that requests might get blocked behind each other such that your new query is queued before you even submitted the previous one. In that case it makes sense to cancel the unsent one (and if very expensive, perhaps when the sent ones), but I don't know that web browsers can tell you whether a request is queued or in-flight or give you meaningful lifecycle hooks. Obviously normal programs have a lot more flexibility in how to handle this. But this is also not the case posited originally, which is low latency/fast processing.
- Arch-TK 1y ago
  The thing about debouncing is that debouncing interrupts from input pins connected directly to e.g. switches is universally a bad idea. Interrupt pins are weird, level change too slowly? You might never see the interrupt trigger or you'll see it trigger more than once. Switch back and forth many times at a high frequency before settling? Again, you might see interrupts for every switch or you might just get nothing at all. (In summary, directly connecting a noisy switch to an interrupt pin will mean you can lose level transition events.) To make this work reliably you either need to debounce in hardware before it reaches your interrupt pin or forego interrupts entirely in favour of polling the input pin at a specific speed and keeping a state history. So the term as it originates in electronics is now both misused and if you do translate it back to electronics it's considered a terrible idea.
jiehong 1y ago
In electronics, I think we'd use a latch, so it switches high, and stays high despite input change. Doesn't really apply to a search box, where it's more of a delayed event if no event during a specific time window, only keeping last event.
- naasking 1y ago
  > In electronics, I think we'd use a latch, so it switches high, and stays high despite input change. RC circuits are more typical, you want to filter out high frequency pulses (indicative of bouncing) and only keep the settled/steady state signal. A latch would be too eager I think.
- kazinator 1y ago
  Switches usually open after closing, so your latch arrangement has to figure out how to unlatch. At which point you are doing debouncing: distinguishing an intentional switch opening from the bounce that continued after you latched. You need some hold-off time or something. Also, switches contacts bounce when opening! A latch could be great for some kind of panic button which indicates a state change that continues to be asserted when the switch opens (and is reset in some other way).
Tade0 1y ago
> One important difference is that if you have unlimited amounts of low latency and processing power, you can do a full search for each keystroke, But you don't want that, as it's useless. Until the user actually finished typing, they're going to have more results than they can meaningfully use - especially that the majority will be irrelevant and just get in the way of real results. The signal in between is actually, really not useful - at least not on first try when the user is not aware what's in the data source and how can they hack the search query to get their results with minimal input.
- maxbond 1y ago
  No one wants to see results for the letter "a", no one wants their database processing that search, and updating the UI while you're typing can be really distracting.
  - meindnoch 1y ago
    >No one wants to see results for the letter "a" Don't make assumptions about what the user may or may not want to search for. E.g. in my music collection I have albums from both !!! [1] and Ø [2]. I've encountered software that "helpfully" prevented me from searching for these artists, because the developers thought that surely noone would search for such terms. _______ [1] https://www.discogs.com/artist/207714- https://www.discogs.com/artist/207714-!!! ← See? The HN link highlighter also thinks that URLs cannot end with !!!. [2] https://www.discogs.com/artist/31887-Ø https://www.discogs.com/artist/31887-Ø
    - simoncion 1y ago
      Let's see if surrounding that URL in the URL-surrounding character pair helps the HN linkifier: <https://www.discogs.com/artist/207714-!!! https://www.discogs.com/artist/207714-!!!> Edit: It does. So, this would be yet another of the squillion-ish examples to support the advice "Please, for the love of god, always enclose your URLs in '<>'.". (And if you're writing a general-purpose URL linkifier, PLEASE just assume that everything between those characters IS part of the URL, rather than assuming you know better than the user.)
Findecanor 1y ago
I agree that this is a bad analogy. I've programmed my own keyboards, mice and game controllers. If you want the fastest response time then you'd make debouncing be asymmetric: report press ("Make") on the first leading edge, and don't report release ("Break") until the signal has been stable for n ms after a trailing edge. That is the opposite of what's done in the blog article. Having a delay on the leading edge is for electrically noisy environments, such as among electric motors and a long wire from the switch to the MCU, where you could potentially get spurious signals that are not from a key press. Debouncing could also be done in hardware without delay, if you have a three-pole switch and an electronic latch. A better analogy would perhaps be "Event Compression": coalescing multiple consecutive events into one, used when producer and consumer are asynchronous. Better but not perfect.
- Sharlin 1y ago
  Debouncing is established terminology in UI and other event-handling stuff at this point, and has been for a decade. It's a bit too late to complain. Language evolves and not all new uses of words are good analogies.
  - em3rgent0rdr 1y ago
    Yeah. It is not too uncommon for terms to refer to how things were done in the past or in another context. For example, we still "dial" a number on our phone even though rotary phones are no longer used...for other examples see https://en.wikipedia.org/wiki/Misnomer#Older_name_retained https://en.wikipedia.org/wiki/Misnomer#Older_name_retained
    - kazinator 1y ago
      That's the same context (making a call to a phone number) with a different implementation.
  - kazinator 1y ago
    > for a decade Whoa!
- 1y ago
haileys 1y ago
Debouncing is a term of art in UI development and has been for a long time. It is analogous to, but of course not exactly the same as, debouncing in electronics.
amelius 1y ago
It's basically debouncing plus edge detection.
jon-wood 1y ago
Search is a bad example there, a better one would have been clicking a button to add an item to a list, or pressing a shortcut key to do so, where you want to only submit that item once even if someone frantically clicks on the button because they're feeling impatient.
- account42 1y ago
  No you should not filter user input like this. Keep user interfaces simple and predictable. If it really only makes sense to perform the action once than disable/remove the button on the first click. If it makes sense to click the button multiple times then there should be no limit to how fast you can do that. It's really infuriating when crappy software drops user input because its too slow to process one input before the next. There is reason why input these days comes in events that are queued and we aren't still checking if the key is up or down in a loop.
  - sgammon 1y ago
    Removing the button from the DOM after click is maybe the worst advice I’ve ever heard for web UX
matthewmacleod 1y ago
Actually I think it's pretty similar to your example. The "intended semantics" of the search action in that sort of field are to search for the text you enter – not to search for the the side-effects of in-progress partial completion. Yes, it's not an exact comparison (hence analogy) – but it's not anything worth getting into a fight about.
- account42 1y ago
  The user intent is usually to get to what they are looking for as quickly as possible. If you intentionally introduce delays by forcing them to enter the complete query or pause to receive intermediate results then you are slowing that down.
  - naasking 1y ago
    > The user intent is usually to get to what they are looking for as quickly as possible. Yes, and returning 30,000 results matching the "a" they just typed is not going to do that. "Getting the desired result fastest" probably requires somewhere between 2 and 10 characters, context-dependent.
- hombre_fatal 1y ago
  Yeah, I don't get how this thread is at the top. You debounce a physical switch because it makes contact multiple times before settling in the contacted position, e.g. you might wait until it's settled before acting, or you act upon the first signal and ignore the ones that quickly follow. And that closely resembles the goal and even implementation of UI debouncing. It also makes sense in a search box because there you have the distinction between intermediate vs. settled state. Do you act on what might be intermediate states, or do you try to assume settled state? Just because it might have a more varied or more abstract meaning in another industry doesn't mean it's a bad analogy, even though Javascript is involved, sheesh.
meindnoch 1y ago
[flagged]
- soulofmischief 1y ago
  What a bitter lens with which to view the world. The reality is that language evolves all the time through specialized use and adoption, web development is no different. Every profession and craft builds a pattern language from both borrowed and new terms. You can explain the phenomenon without patronizing and insulting anyone who works on frontend code.
- Sharlin 1y ago
  You seem to have no idea of how language works, and has worked for as long as there has been language.
bravesoul2 1y ago
I like you said obnoxious... it is assumed this behaviour is what people want rather than just press a button or hit enter when ready.
account42 1y ago
It's also worth mentioning that real debouncing doesn't always have to depend on time when you have an analog signal. Instead you could have different thresholds for going from stat A to B vs going from B to A with enough distance between those threshold that you won't switch back and forth during an event. This can even be implemented physically in the switch itself by having separate ON and OFF contacts.
davnicwil 1y ago
Thank you for this comment! Suddenly 'bouncing' makes total sense as a mental image when before it only vaguely tracked in some abstract way about tons of tiny events bouncing around and triggering things excitedly until you contain them with debounce() :-) Come to think of it throttle is the much easier to understand analogy.
- Izkata 1y ago
  Throttling is a different thing though. Debouncing is waiting until the input has stopped occurring so it can run on the final result, throttling is running immediately on the first input and blocking further input for a short duration.
  - davnicwil 1y ago
    thanks - I know :-) ambiguous phrasing! Just saying of the two throttling is the one that has the more well-known physical analogy
kube-system 1y ago
It's a word borrowed for a similar concept. This is so common in software, it is basically the norm. There are hundreds of analogistic terms in software.
rayiner 1y ago
It’s still a top 10% analogy.
nottorp 1y ago
> if you have unlimited amounts of low latency and processing power And battery, or at least enough air conditioning to cool down the desktop because of those extraneous operations, right?

maxbond 1y ago

It's the term used in frontend dev. It is actually a little worse than you're imagining, because we're not sampling, we're receiving callbacks (so more analogous to interrupts than sampling in a loop). Eg the oninput callback. I've used it for implementing auto save without making a localStorage call on every key press, for example. I think it makes sense if you view it from a control theory perspective rather than an embedded perspective. The mechanics of the UI (be that a physical button or text input) create a flaggy signal. Naively updating the UI on that signal would create jank. So we apply some hysteresis to obtain a clean signal. In the day way that acting 50 times on a single button press is incorrect behavior, saving (or searching or what have you) 50 times from typing a single sentence isn't correct (or at least undesired). The example of 10ms is way too low though, anything less than 250ms seems needlessly aggressive to me. 250ms is still going to feel very snappy. I think if you're typing at 40-50wpm you'll probably have an interval of 100-150ms between characters, so 10ms is hardly debouncing anything.

Findecanor 1y ago
An office keyboard's own debouncing could delay a key press 30 ms, and then the OS, software and graphics/monitor hardware would delay it just as much before the user could see the character on screen. So, indeed, 10 ms is much too low.
- maxbond 1y ago
  Perhaps the people at MDN are 10x typists, with competition-grade gaming keyboards.
- mindslight 1y ago
  No, correct debouncing of a hardware button should not add any delay to a single press. It's not wait-then-act, but rather act-then-wait-to-act-again. You're probably thinking of a polling interval (often exacerbated by having key switches wired in a matrix rather than one per pin).
  - maxbond 1y ago
    They describe that approach in another comment [1], so I take it to be a descriptive statement about low end keyboards. Perhaps the engineers designing these keyboards view 30ms as an acceptable latency to prevent spurious key presses. [1] https://news.ycombinator.com/item?id=44822183 https://news.ycombinator.com/item?id=44822183
  - kazinator 1y ago
    The bouncing behavior itself adds delay. If it takes 30 ms for the switch to settle to a state where it is considered closed according to the debouncing algorithm's parameters, then that's what it is. The algorithm might be "sample every millisecond, until 9 out of 10 samples show "closed". That imposes a minimum delay of 10 ms, and the maximum is whatever it takes for that criterion to be reached.
    - mindslight 1y ago
      That's a low pass filter. And I suppose in the type of highly-resilient slow changing signals like OP mentioned in a different comment, it makes sense to do that and even to refer to it as "debouncing". But for general consumer electronic devices with basic local buttons, the standard algorithm is something more like act on the first close, then ignore the next 10 samples. When there is no other reason for a switch to read as closed, the first close means the button has definitely been pushed. The point of debouncing is to avoid seeing the open-close-open-close oscillation afterwards (contacts settling) as their own release-press combos.
zeta0134 1y ago
Additionally, regardless of naming, debouncing is an accessibility feature for a surprisingly large portion of the population. Many users who grew up with double-click continue to attempt to provide this input on web forms, because it mostly works. Many more with motor control issues may struggle to issue just a single click reliably, especially on a touchscreen.
- gibsonsmog 1y ago
  Holy moly, for years I've had in the back of my head this thought about why, earlier in my career, I'd see random doubly submitted form submissions on certain projects. Same form code and processing as other sites, legitimate submissions too. Eventually we added more spam filtering and restrictions unrelated to these legitimate ones, but it was probably the double-click users causing those errant submissions. I'd never even have thought of those users. Fascinating
  - Sharlin 1y ago
    Yes, it's something pretty much all UI frameworks end up implementing. The easiest way to do it is to simply disable the button at first click until the request is complete. This, of course, also prevents double submissions in cases the user doesn't get enough feedback and clicks again to make sure something actually happened.
    - deleted 1y ago
      [deleted]
  - kazinator 1y ago
    Users of GUI operating systems had been trained to double-click on icons representing applications or files in order to launch them. If you make a web UI in which a button is styled via an icon image (or otherwise) to look like a launchable application or file, those users will double click on it. If you make it look like a button, they won't; they were certainly not trained to double-click on [OK] or [Cancel] in an OK/Cancel dialog box, for instance! Double clicking to launch an action on a file makes sense because you need single click for selecting it. There are things you can do with it other than launch, like dragging it to another location. T;DR: don't make buttons look like elements that can be selected and dragged somewhere? -- Another reason: I've sometimes multiply clicked on some button-like thing in a web UI because in spite of working fine, it made no indication that had received the click! It was styled to look like a button in the unclicked state ... and that one image was all it had. To detect that the action launched you have to look for clues in the browser status areas showing that something is being loaded. Those are often made unobtrusive these days. Gone are the days of Netscape's spinning planet. When the user sees that a button doesn't change state upon being clicked, yet the normal cursor is seen (pointer, not hourglass or spinning thing or whatever) they assume that the application has become unresponsive due to a bug or performance problem, or that somehow the click event was dropped; maybe their button is physically not working or whatever.
account42 1y ago
> 250ms is still going to feel very snappy WTF no it won't.
- schwartzworld 1y ago
  For the kind of behaviors they are describing it would. An extra 250ms waiting for an app to load is a lot, but for something like the described autosave behavior, waiting for a 250ms pause in typing before autosaving or making a fetch call is pretty snappy.
- maxbond 1y ago
  What value would you recommend?
deleted 1y ago
[deleted]
ndriscoll 1y ago
Why would e.g. saving after each keypress be janky from the UI perspective? These days disks can complete a write in 20 us. If you're typing at 0.1 seconds/character, you're going 5,000 times slower than the computer is capable of. If you have a 60 Hz monitor, it can block saving your work every frame and still be 99.9% idle. Even if you're making network requests each time, if the request finishes in 20 ms, you're still done 80 ms before the user presses the next button.
- schwartzworld 1y ago
  Local storage is a poor example because it updates in the background and wouldn’t necessarily change your UI much. But if a design calls for a search to be made while a user types that would get janky fast. React in particular is data driven so in the above example, if you make the api call on each keypress, and save it into state or whatever, the UI will update automatically. I can type 70 words per minute. Nobody wants the search results to update that fast. (Should we be building searches that work this way? Often you have no choice.) A slow network + a short search string + a not top of the line device like a cheap phone means a really janky experience. And even if it’s not janky, its a waste of your users bandwidth (not everybody has unlimited) and an unnecessary drain on your server resources. Even though we say “update as the user types” people type in bursts. There’s no reason not to debounce it, and if you can make the debounce function composable, you can reuse it all over the place. It’s a courtesy to the users and a good practice.
  - maxbond 1y ago
    Introducing auto save into the discussion may have been confusing, you're both right that that wouldn't generally cause jank, debouncing an auto save is more about not using resources unnecessarily and may help provide a better edit history depending on how you've written the application.
  - ndriscoll 1y ago
    I type around 90-100 wpm and I appreciate that clementine player for example doesn't seem to have any delay except apparently when querying radio stations (which is described as "to be polite"). When searching your own library, it updates immediately (I'd be very surprised if the query weren't faster than my monitor refresh). My only perception is that it's fast. I don't know why anyone would see it as janky. So it seems to me that it's entirely about not wasting resources/to be polite. In the limit where you have a computer that can do its work faster than your display refreshes, letting it do so seems to clearly make everything feel snappier. No one's typing quickly on a phone anyway and most people probably do a word at a time, and that word will come in slower than your denounce, so again there is no point in delaying it. One thing another user pointed out is that your search does need to be stable. An exact substring match shouldn't randomly get bumped down as you type more. A separate issue you might encounter for slow queries is that requests might get blocked behind each other such that your new query is queued before you even submitted the previous one. In that case it makes sense to cancel the unsent one (and if very expensive, perhaps when the sent ones), but I don't know that web browsers can tell you whether a request is queued or in-flight or give you meaningful lifecycle hooks. Obviously normal programs have a lot more flexibility in how to handle this. But this is also not the case posited originally, which is low latency/fast processing.
Arch-TK 1y ago
The thing about debouncing is that debouncing interrupts from input pins connected directly to e.g. switches is universally a bad idea. Interrupt pins are weird, level change too slowly? You might never see the interrupt trigger or you'll see it trigger more than once. Switch back and forth many times at a high frequency before settling? Again, you might see interrupts for every switch or you might just get nothing at all. (In summary, directly connecting a noisy switch to an interrupt pin will mean you can lose level transition events.) To make this work reliably you either need to debounce in hardware before it reaches your interrupt pin or forego interrupts entirely in favour of polling the input pin at a specific speed and keeping a state history. So the term as it originates in electronics is now both misused and if you do translate it back to electronics it's considered a terrible idea.

jiehong 1y ago

In electronics, I think we'd use a latch, so it switches high, and stays high despite input change. Doesn't really apply to a search box, where it's more of a delayed event if no event during a specific time window, only keeping last event.

naasking 1y ago
> In electronics, I think we'd use a latch, so it switches high, and stays high despite input change. RC circuits are more typical, you want to filter out high frequency pulses (indicative of bouncing) and only keep the settled/steady state signal. A latch would be too eager I think.
kazinator 1y ago
Switches usually open after closing, so your latch arrangement has to figure out how to unlatch. At which point you are doing debouncing: distinguishing an intentional switch opening from the bounce that continued after you latched. You need some hold-off time or something. Also, switches contacts bounce when opening! A latch could be great for some kind of panic button which indicates a state change that continues to be asserted when the switch opens (and is reset in some other way).

Tade0 1y ago

> One important difference is that if you have unlimited amounts of low latency and processing power, you can do a full search for each keystroke, But you don't want that, as it's useless. Until the user actually finished typing, they're going to have more results than they can meaningfully use - especially that the majority will be irrelevant and just get in the way of real results. The signal in between is actually, really not useful - at least not on first try when the user is not aware what's in the data source and how can they hack the search query to get their results with minimal input.

maxbond 1y ago
No one wants to see results for the letter "a", no one wants their database processing that search, and updating the UI while you're typing can be really distracting.
- meindnoch 1y ago
  >No one wants to see results for the letter "a" Don't make assumptions about what the user may or may not want to search for. E.g. in my music collection I have albums from both !!! [1] and Ø [2]. I've encountered software that "helpfully" prevented me from searching for these artists, because the developers thought that surely noone would search for such terms. _______ [1] https://www.discogs.com/artist/207714- https://www.discogs.com/artist/207714-!!! ← See? The HN link highlighter also thinks that URLs cannot end with !!!. [2] https://www.discogs.com/artist/31887-Ø https://www.discogs.com/artist/31887-Ø
  - simoncion 1y ago
    Let's see if surrounding that URL in the URL-surrounding character pair helps the HN linkifier: <https://www.discogs.com/artist/207714-!!! https://www.discogs.com/artist/207714-!!!> Edit: It does. So, this would be yet another of the squillion-ish examples to support the advice "Please, for the love of god, always enclose your URLs in '<>'.". (And if you're writing a general-purpose URL linkifier, PLEASE just assume that everything between those characters IS part of the URL, rather than assuming you know better than the user.)

Findecanor 1y ago

I agree that this is a bad analogy. I've programmed my own keyboards, mice and game controllers. If you want the fastest response time then you'd make debouncing be asymmetric: report press ("Make") on the first leading edge, and don't report release ("Break") until the signal has been stable for n ms after a trailing edge. That is the opposite of what's done in the blog article. Having a delay on the leading edge is for electrically noisy environments, such as among electric motors and a long wire from the switch to the MCU, where you could potentially get spurious signals that are not from a key press. Debouncing could also be done in hardware without delay, if you have a three-pole switch and an electronic latch. A better analogy would perhaps be "Event Compression": coalescing multiple consecutive events into one, used when producer and consumer are asynchronous. Better but not perfect.

Sharlin 1y ago
Debouncing is established terminology in UI and other event-handling stuff at this point, and has been for a decade. It's a bit too late to complain. Language evolves and not all new uses of words are good analogies.
- em3rgent0rdr 1y ago
  Yeah. It is not too uncommon for terms to refer to how things were done in the past or in another context. For example, we still "dial" a number on our phone even though rotary phones are no longer used...for other examples see https://en.wikipedia.org/wiki/Misnomer#Older_name_retained https://en.wikipedia.org/wiki/Misnomer#Older_name_retained
  - kazinator 1y ago
    That's the same context (making a call to a phone number) with a different implementation.
- kazinator 1y ago
  > for a decade Whoa!
1y ago

haileys 1y ago

Debouncing is a term of art in UI development and has been for a long time. It is analogous to, but of course not exactly the same as, debouncing in electronics.

amelius 1y ago

It's basically debouncing plus edge detection.

jon-wood 1y ago

Search is a bad example there, a better one would have been clicking a button to add an item to a list, or pressing a shortcut key to do so, where you want to only submit that item once even if someone frantically clicks on the button because they're feeling impatient.

account42 1y ago
No you should not filter user input like this. Keep user interfaces simple and predictable. If it really only makes sense to perform the action once than disable/remove the button on the first click. If it makes sense to click the button multiple times then there should be no limit to how fast you can do that. It's really infuriating when crappy software drops user input because its too slow to process one input before the next. There is reason why input these days comes in events that are queued and we aren't still checking if the key is up or down in a loop.
- sgammon 1y ago
  Removing the button from the DOM after click is maybe the worst advice I’ve ever heard for web UX

matthewmacleod 1y ago

Actually I think it's pretty similar to your example. The "intended semantics" of the search action in that sort of field are to search for the text you enter – not to search for the the side-effects of in-progress partial completion. Yes, it's not an exact comparison (hence analogy) – but it's not anything worth getting into a fight about.

account42 1y ago
The user intent is usually to get to what they are looking for as quickly as possible. If you intentionally introduce delays by forcing them to enter the complete query or pause to receive intermediate results then you are slowing that down.
- naasking 1y ago
  > The user intent is usually to get to what they are looking for as quickly as possible. Yes, and returning 30,000 results matching the "a" they just typed is not going to do that. "Getting the desired result fastest" probably requires somewhere between 2 and 10 characters, context-dependent.
hombre_fatal 1y ago
Yeah, I don't get how this thread is at the top. You debounce a physical switch because it makes contact multiple times before settling in the contacted position, e.g. you might wait until it's settled before acting, or you act upon the first signal and ignore the ones that quickly follow. And that closely resembles the goal and even implementation of UI debouncing. It also makes sense in a search box because there you have the distinction between intermediate vs. settled state. Do you act on what might be intermediate states, or do you try to assume settled state? Just because it might have a more varied or more abstract meaning in another industry doesn't mean it's a bad analogy, even though Javascript is involved, sheesh.

meindnoch 1y ago

[flagged]

soulofmischief 1y ago
What a bitter lens with which to view the world. The reality is that language evolves all the time through specialized use and adoption, web development is no different. Every profession and craft builds a pattern language from both borrowed and new terms. You can explain the phenomenon without patronizing and insulting anyone who works on frontend code.
Sharlin 1y ago
You seem to have no idea of how language works, and has worked for as long as there has been language.

bravesoul2 1y ago

I like you said obnoxious... it is assumed this behaviour is what people want rather than just press a button or hit enter when ready.

account42 1y ago

It's also worth mentioning that real debouncing doesn't always have to depend on time when you have an analog signal. Instead you could have different thresholds for going from stat A to B vs going from B to A with enough distance between those threshold that you won't switch back and forth during an event. This can even be implemented physically in the switch itself by having separate ON and OFF contacts.

davnicwil 1y ago

Thank you for this comment! Suddenly 'bouncing' makes total sense as a mental image when before it only vaguely tracked in some abstract way about tons of tiny events bouncing around and triggering things excitedly until you contain them with debounce() :-) Come to think of it throttle is the much easier to understand analogy.

Izkata 1y ago
Throttling is a different thing though. Debouncing is waiting until the input has stopped occurring so it can run on the final result, throttling is running immediately on the first input and blocking further input for a short duration.
- davnicwil 1y ago
  thanks - I know :-) ambiguous phrasing! Just saying of the two throttling is the one that has the more well-known physical analogy

kube-system 1y ago

It's a word borrowed for a similar concept. This is so common in software, it is basically the norm. There are hundreds of analogistic terms in software.

rayiner 1y ago

It’s still a top 10% analogy.

nottorp 1y ago

> if you have unlimited amounts of low latency and processing power And battery, or at least enough air conditioning to cool down the desktop because of those extraneous operations, right?