How do I check if an element is really visible with JavaScript

Question

In JavaScript  how would you check if an element is actually visible   I don t just mean checking the visibility and display attributes  I mean  checking that the element is not   visibility  hidden or display  none underneath another element scrolled off the edge of the screen   For technical reasons I can t include any scripts  I can however use Prototype as it is on the page already

User · Answer

Prototype s Element library is one of the most powerful query libraries in terms of the methods  I recommend you to check out the API   A few hints    Checking visibility can be a pain  but you can use the Element getStyle   method and Element visible   methods combined into a custom function  With getStyle   you can check the actual computed style  I don t know exactly what you mean by  underneath     If you meant by it has a specific ancestor  for example  a wrapper div  you can use Element up cssRule    var child      myparagraph    if  child up  mywrapper          I lost my mom    else        I found my mom      If you want to check the siblings of the child element you can do that too   var child      myparagraph    if  child previous  mywrapper          I lost my bro     else        I found my bro     Again  Element lib can help you if I understand correctly what you mean    You can check the actual dimensions of the viewport and the offset of your element so you can calculate if your element is  off screen     Good luck   I pasted a test case for prototypejs at http   gist github com 117125  It seems in your case we simply cannot trust in getStyle   at all  For maximizing the reliability of the isMyElementReallyVisible function you should combine the following    Checking the computed style  dojo has a nice implementation that you can borrow  Checking the viewportoffset  prototype native method  Checking the z-index for the  beneath  problem  under Internet nbsp Explorer it may be buggy

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Catch mouse-drag and viewport events  onmouseup  onresize  onscroll     When a drag ends do a comparison of the dragged item boundary with all  elements of interest   ie  elements with class  dont hide  or an array of ids   Do the same with window onscroll and window onresize  Mark any elements hidden with a special attribute or classname or simply perform whatever action you want then and there   The hidden tests are pretty easy  For  totally hidden  you want to know if ALL corners are either inside the dragged-item boundary or outside the viewport  For partially hidden you re looking for a single corner matching the same test

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Check elements  offsetHeight property  If it is more than 0  it is visible  Note  this approach doesn t cover a situation when visibility hidden style is set  But that style is something weird anyways

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I don t know how much of this is supported in older or not-so-modern browsers  but I m using something like this  without the neeed for any libraries    function visible element      if  element offsetWidth     0    element offsetHeight     0  return false    var height   document documentElement clientHeight        rects   element getClientRects          on top   function r            var x    r left   r right  2  y    r top   r bottom  2          return document elementFromPoint x  y      element             for  var i   0  l   rects length  i  lt  l  i          var r   rects i           in viewport   r top  gt  0   r top  lt   height    r bottom  gt  0  amp  amp  r bottom  lt   height       if  in viewport  amp  amp  on top r   return true        return false      It checks that the element has an area   0 and then it checks if any part of the element is within the viewport and that it is not hidden  under  another element  actually I only check on a single point in the center of the element  so it s not 100  assured -- but you could just modify the script to itterate over all the points of the element  if you really need to       Update  Modified on top function that check every pixel   on top   function r      for  var x   Math floor r left   x max   Math ceil r right   x  lt   x max  x      for  var y   Math floor r top   y max   Math ceil r bottom   y  lt   y max  y          if  document elementFromPoint x  y      element  return true        return false       Don t know about the performance

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One way to do it is   isVisible elm        while elm tagName     BODY             if    elm  visible    return false          elm   elm parentNode            return true      Credits  https   github com atetlaw Really-Easy-Field-Validation blob master validation js L178

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As jkl pointed out  checking the element s visibility or display is not enough  You do have to check its ancestors  Selenium does this when it verifies visibility on an element   Check out the method Selenium prototype isVisible in the selenium-api js file   http   svn openqa org svn selenium-on-rails selenium-on-rails selenium-core scripts selenium-api js

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Here is a sample script and test case   Covers positioned elements  visibilty  hidden  display  none   Didn t test z-index  assume it works    lt  DOCTYPE HTML PUBLIC  -  W3C  DTD HTML 4 01 Transitional  EN   http   www w3 org TR html4 loose dtd  gt   lt html gt     lt head gt       lt title gt  lt  title gt       lt style type  text css  gt      div         width  200px        border  1px solid red            p         border  2px solid green             r         border  1px solid  BB3333        background   EE9999        position  relative        top  -50px        height  2em             of         overflow  hidden        height  2em        word-wrap  none              of p         width  100               of pre         display  inline             iv         visibility  hidden             dn         display  none             lt  style gt       lt script src  http   www prototypejs org assets 2008 9 29 prototype-1 6 0 3 js  gt  lt  script gt       lt script gt        function isVisible elem           if  Element getStyle elem   visibility       hidden     Element getStyle elem   display       none               return false                    var topx  topy  botx  boty          var offset   Element positionedOffset elem           topx   offset left          topy   offset top          botx   Element getWidth elem    topx          boty   Element getHeight elem    topy          var v   false          for  var x   topx  x  lt   botx  x                for var y   topy  y  lt   boty  y                  if  document elementFromPoint x y     elem                     item is visible               v   true                break                                      if  v    true                break                                return v                 window onload function             var es   Element descendants  body            for  var i   0  i  lt  es length  i                 if   isVisible es i                  alert es i  tagName                                      lt  script gt     lt  head gt     lt body id  body  gt       lt div class  s  gt  lt p gt This is text lt  p gt  lt p gt More text lt  p gt  lt  div gt       lt div class  r  gt This is relative lt  div gt       lt div class  of  gt  lt p gt This is too wide    lt  p gt  lt pre gt hidden lt  pre gt       lt div class  iv  gt This is invisible lt  div gt       lt div class  dn  gt This is display none lt  div gt     lt  body gt   lt  html gt

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Try element getBoundingClientRect    It will return an object with properties   bottom top right left width  --  browser dependent height -- browser dependent   Check that the width and height of the element s BoundingClientRect are not zero which is the value of hidden or non-visible elements  If the values are greater than zero the element should be visible in the body  Then check if the bottom property is less than screen height which would imply that the element is withing the viewport   Technically you would also have to account for the top of the browser window including the searchbar  buttons  etc

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Checks display and visibility of elements and it s parents     param  DomElement  el     param  boolean isDeep Watch parents  Default is true     return  Boolean         author Oleksandr Knyga  lt oleksandrknyga gmail com gt      function isVisible el  isDeep        var elIsVisible   true       if  undefined      typeof isDeep            isDeep   true             elIsVisible   elIsVisible  amp  amp  el offsetWidth  gt  0  amp  amp  el offsetHeight  gt  0       if isDeep  amp  amp  elIsVisible             while  BODY     el tagName  amp  amp  elIsVisible                elIsVisible   elIsVisible  amp  amp   hidden     window getComputedStyle el  visibility              el   el parentElement                       return elIsVisible

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This is what I have so far  It covers both 1 and 3  I m however still struggling with 2 since I m not that familiar with Prototype  I m more a jQuery type of guy    function isVisible  elem         var  elem     elem           First check if elem is hidden through css as this is not very costly      if   elem getStyle  display       none      elem getStyle  visibility       hidden                elem is set through CSS stylesheet or inline to invisible         return false               Now check for the elem being outside of the viewport     var  elemOffset    elem viewportOffset        if   elemOffset left  lt  0     elemOffset top  lt  0              elem is left of or above viewport         return false            var vp   document viewport getDimensions        if   elemOffset left  gt  vp width     elemOffset top  gt  vp height              elem is below or right of vp         return false               Now check for elements positioned on top        TODO  Build check for this using Prototype          Neither of these was true  so the elem was visible      return true

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For the point 2  I see that no one has suggested to use document elementFromPoint x y   to me it is the fastest way to test if an element is nested or hidden by another  You can pass the offsets of the targetted element to the function  Here s PPK test page on elementFromPoint  From MDN s documentation   The elementFromPoint   method   available on both the Document and ShadowRoot objects   returns the topmost Element at the specified coordinates  relative to the viewport

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Interesting question   This would be my approach    At first check that element style visibility      hidden   amp  amp  element style display      none  Then test with document elementFromPoint element offsetLeft  element offsetTop  if the returned element is the element I expect  this is tricky to detect if an element is overlapping another completely  Finally test if offsetTop and offsetLeft are located in the viewport taking scroll offsets into account    Hope it helps

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I don t think checking the element s own visibility and display properties is good enough for requirement  1  even if you use currentStyle getComputedStyle   You also have to check the element s ancestors   If an ancestor is hidden  so is the element

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Here is a part of the response that tells you if an element is in the viewport  You may need to check if there is nothing on top of it using elementFromPoint  but it s a bit longer   function isInViewport element      var rect   element getBoundingClientRect      var windowHeight   window innerHeight    document documentElement clientHeight    var windowWidth   window innerWidth    document documentElement clientWidth     return rect bottom  gt  0  amp  amp  rect top  lt  windowHeight  amp  amp  rect right  gt  0  amp  amp  rect left  lt  windowWidth

User · Answer

You can use the clientHeight or clientWidth properties  function isViewable element     return  element clientHeight  gt  0

[javascript] How do I check if an element is really visible with JavaScript?

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