Check if a key is down

Question

Is there a way to detect if a key is currently down in JavaScript   I know about the  keydown  event  but that s not what I need  Some time AFTER the key is pressed  I want to be able to detect if it is still pressed down   P  S  The biggest issue seems to be that after some period of time the key begins to repeat  firing off keydown and keyup events like a fiend  Hopefully there is just a simple isKeyDown key  function  but if not then this issue will need to be overcome   worked around

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The following code is what I m using   var altKeyDownCount   0  window onkeydown   function  e        if   e  e   window event      if  e altKey            altKeyDownCount            if  30  lt  altKeyDownCount                    key   removeClass  hidden                altKeyDownCount   0                    return false           window onkeyup   function  e        if   e  e   window event      altKeyDownCount   0          key   addClass  hidden        When the user keeps holding down the Alt key for some time  about 2 seconds   a group of labels  class  key hidden   appears  When the Alt key is released  the labels disappear  jQuery and Bootstrap are both used

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Is there a way to detect if a key is currently down in JavaScript    Nope  The only possibility is monitoring each keyup and keydown and remembering      after some period of time the key begins to repeat  firing off keydown and keyup events like a fiend    It shouldn t  You ll definitely get keypress repeating  and in many browsers you ll also get repeated keydown  but if keyup repeats  it s a bug   Unfortunately it is not a completely unheard-of bug  on Linux  Chromium  and Firefox  when it is being run under GTK   which it is in popular distros such as Ubuntu  both generate repeating keyup-keypress-keydown sequences for held keys  which are impossible to distinguish from someone hammering the key really fast

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Ended up here to check if there was something builtin to the browser already  but it seems there isn t  This is my solution  very similar to Robert s answer     use strict    const is key down         gt        const state            window addEventListener  keyup    e    gt  state e key    false       window addEventListener  keydown    e    gt  state e key    true        return  key    gt  state hasOwnProperty key   amp  amp  state key     false          You can then check if a key is pressed with is key down  ArrowLeft

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I scanned the above answers and the proposed keydown keyup approach works only under special circumstances  If the user alt-tabs away  or uses a key gesture to open a new browser window or tab  then a keydown will be registered  which is fine  because at that point it s impossible to tell if the key is something the web app is monitoring  or is a standard browser or OS shortcut  Coming back to the browser page  it ll still think the key is held  though it was released in the meantime  Or some key is simply kept held  while the user is switching to another tab or application with the mouse  then released outside our page   Modifier keys  Shift etc   can be monitored via mousemove etc  assuming that there is at least one mouse interaction expected when tabbing back  which is frequently the case   For most all other keys  except modifiers  Tab  Delete  but including Space  Enter   monitoring keypress would work for most applications - a key held down will continue to fire  There s some latency in resetting the key though  due to the periodicity of keypress firing  Basically  if keypress doesn t keep firing  then it s possible to rule out most of the keys  This  combined with the modifiers is pretty airtight  though I haven t explored what to do with Tab and Backspace   I m sure there s some library out there that abstracts over this DOM weakness  or maybe some DOM standard change took care of it  since it s a rather old question

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My solution   var pressedKeys       window onkeyup   function e    pressedKeys e keyCode    false    window onkeydown   function e    pressedKeys e keyCode    true      I can now check if any key is pressed anywhere else in the script by checking  pressedKeys  code of the key     If it s true  the key is pressed

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mytextbox   keydown function  e                if  e keyCode    13                    if  e altKey                        alert  alt is pressed                                           if you press alt   enter  you will see the alert

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In addition to using keyup and keydown listeners to track when is key goes down and back up  there are actually some properties that tell you if certain keys are down   window onmousemove   function  e      if   e  e   window event    if  e shiftKey     shift is down      if  e altKey     alt is down      if  e ctrlKey     ctrl is down      if  e metaKey     cmd is down        This are available on all browser generated event objects  such as those from keydown  keyup  and keypress  so you don t have to use mousemove   I tried generating my own event objects with document createEvent  KeyboardEvent   and document createEvent  KeyboardEvent   and looking for e shiftKey and such  but I had no luck   I m using Chrome 17 on Mac

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I don t believe there is anything like an isKeyDown function  but you could write your own   Basically  create an array whose length is the number of keys you want to monitor  Then using the documents pages controls keyUp and keyDown events  update the array with that key s state   Then write a function that checks if a certain key is down and returns a bool   var keyEnum     W Key 0  A Key 1  S Key 2  D Key 3    var keyArray   new Array 4    function onKeyDown            Detect which key was pressed     if  key     w            keyArray keyEnum W Key    true         Repeat for each key you care about       function onKeyUp            Detect which key was released     if  key     w            keyArray keyEnum W Key    false         Repeat for each key you care about       function isKeyDown key        return keyArray key       That should accomplish what you want

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This works in Firefox and Chrome  I had a need to open a special html file locally  by pressing Enter when the file is selected in the file explorer in Windows   either just for viewing the file or for editing it in a special online editor  So I wanted to distinguish between these two options by holding down the Ctrl-key or not  while pressing Enter  As you all have understood from all the answers here  this seems to be not really possible  but here is a way that mimics this behaviour in a way that was acceptable for me  The way this works is like this  If you hold down the Ctrl-key when opening the file then a keydown event will never fire in the javascript code  But a keyup event will fire  when you finally release the Ctrl-key   The code captures that  The code also turns off keyevents  both keyup and keydown  as soon as one of them occurs  So if you press the Ctrl-key after the file has opened  nothing will happen  window onkeyup   up  window onkeydown   down  function up e      if  e key      F5   return     if you want this to work also on reload with F5     window onkeyup   null    window onkeyup   null    if  e key      Control         alert  Control key was released  You must have held it down while opening the file  so we will now load the file into the editor                    function down       window onkeyup   null    window onkeyup   null

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I know this is very old question  however there is a very lightweight    5Kb  JavaScript library that effectively  patches  the inconsistent firing of keyboard event handlers when using the DOM API   The library is Keydrown   Here s the operative code sample that has worked well for my purposes by just changing the key on which to set the listener   kd P down function        console log  The  P  key is being held down          kd P up function        console clear            This update loop is the heartbeat of Keydrown kd run function        kd tick          I ve incorporated Keydrown into my client-side JavaScript for a proper pause animation in a Red Light Green Light game I m writing  You can view the entire game here   Note  If you re reading this in the future  the game should be code complete and playable  -D    I hope this helps

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Tracks what keys are currently down on the keyboard     function keyboard module onUpdate       var kb           var unicode mapping           document onkeydown   function e           var unicode e charCode  e charCode   e keyCode         var key   getKey unicode           kb key    true          if onUpdate               onUpdate kb                        document onkeyup   function e           var unicode e charCode  e charCode   e keyCode         var key   getKey unicode           delete kb key           if onUpdate               onUpdate kb                        function getKey unicode           if unicode mapping unicode                var key   unicode mapping unicode            else              var key  unicode mapping unicode    String fromCharCode unicode                     return key            return kb     function testing kb       console log  These are the down keys   kb       var keyboard   keyboard module testing           somewhere else in the code if keyboard  K      do something special

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Other people have asked this kind of question before  though I don t see any obvious dupes here right now    I think the answer is that the keydown event  and its twin keyup  are all the info you get  Repeating is wired pretty firmly into the operating system  and an application program doesn t get much of an opportunity to query the BIOS for the actual state of the key   What you can do  and perhaps have to if you need to get this working  is to programmatically de-bounce the key  Essentially  you can evaluate keydown and keyup yourself but ignore a keyupevent if it takes place too quickly after the last keydown    or essentially  you should delay your response to keyup long enough to be sure there s not another keydown event following with something like 0 25 seconds of the keyup   This would involve using a timer activity  and recording the millisecond times for previous events  I can t say it s a very appealing solution  but

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I know it s to late  but I have a lightweight  398 bytes  script that returns if a key is being pressed  https   github com brunoinds isKeyPressed if  KeyPressing isKeyPressed 13      Pass the keyCode integer as parameter      console log  The Enter key is being pressed       else       console log  The Enter key is NOT being pressed         You can even set a interval to check if the key is being pressed  setInterval      gt        if  KeyPressing isKeyPressed 13            console log  The Enter key is being pressed         else          console log  The Enter key is NOT being pressed               1000    Update data every 1000ms  1 second

[javascript] Check if a key is down?

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