JavaScript DOM Find Element Index In Container

Question

I need to find an index of element inside its container by object reference  Strangely  I cannot find an easy way  No jQuery please - only DOM   UL  LI  LI  LI - my index is 2  LI   Yes  I could assign IDs to each element and loop through all nodes to match the ID but it seems a bad solution  Isn t there something nicer    So  say I have an object reference to the third LI as in the example above  How do I know it is index 2   Thanks

User · Answer

You can iterate through the  lt li gt s in the  lt ul gt  and stop when you find the right one   function getIndex li        var lis   li parentNode getElementsByTagName  li        for  var i   0  len   lis length  i  lt  len  i              if  li     lis i                 return i                       Demo

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An example of making an array from HTMLCollection   lt ul id  myList  gt       lt li gt 0 lt  li gt       lt li gt 1 lt  li gt       lt li gt 2 lt  li gt       lt li gt 3 lt  li gt       lt li gt 4 lt  li gt   lt  ul gt    lt script gt  var tagList        var ulList   document getElementById  myList     var tags     ulList getElementsByTagName  li       Dump elements into Array while  tagList length    tags length       tagList push tags tagList length       tagList forEach function item           item addEventListener  click   function  event                console log tagList indexOf  event target    event srcElement                      lt  script gt

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Array prototype indexOf call this parentElement children  this     Or use let statement

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If you want to write this compactly all you need is   var i   0  for   yourElement parentNode i    yourElement i      indexOfYourElement   i    We just cycle through the elements in the parent node  stopping when we find your element You can also easily do   for   yourElement parentNode getElementsByTagName  li   i    yourElement i        if that s all you want to look through

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Here is how I do  2018 version       const index       el parentElement children  indexOf el     Tadaaaam  And  if ever you want to consider raw text nodes too  you can do this instead    const index       el parentElement childNodes  indexOf el     I spread the children into an array as they are an HTMLCollection  thus they do not work with indexOf    Be careful that you are using Babel or that browser coverage is sufficient for what you need to achieve  thinkings about the spread operator which is basically an Array from behind the scene

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2017 update  The original answer below assumes that the OP wants to include non-empty text node and other node types as well as elements  It doesn t seem clear to me now from the question whether this is a valid assumption   Assuming instead you just want the element index  previousElementSibling is now well-supported  which was not the case in 2012  and is the obvious choice now  The following  which is the same as some other answers here  will work in everything major except IE  lt   8   function getElementIndex node        var index   0      while    node   node previousElementSibling              index              return index      Original answer  Just use previousSibling until you hit null  I m assuming you want to ignore white space-only text nodes  if you want to filter other nodes then adjust accordingly   function getNodeIndex node        var index   0      while    node   node previousSibling              if  node nodeType    3        s    test node data                 index                        return index

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You could make usage of Array prototype indexOf  For that  we need to somewhat  cast  the HTMLNodeCollection into a true Array  For instance   var nodes   Array prototype slice call  document getElementById  list   children      Then we could just call   nodes indexOf  liNodeReference      Example    x000D   x000D  var nodes   Array prototype slice call  document getElementById  list   children    x000D      liRef   document getElementsByClassName  match   0   x000D   x000D  console log  nodes indexOf  liRef      x000D   lt ul id  list  gt  x000D       lt li gt foo lt  li gt  x000D       lt li class  match  gt bar lt  li gt  x000D       lt li gt baz lt  li gt      x000D   lt  ul gt  x000D   x000D   x000D

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Just pass the object reference to the following function and you will get the index  function thisindex elm          var the li   elm       var the ul   elm parentNode       var li list   the ul childNodes        var count   0     Tracks the index of LI nodes         Step through all the child nodes of the UL     for  var i   0  i  lt  li list length  i                   var node   li list item i           if  node                        Check to see if the node is a LI             if  node nodeName     LI                                 Increment the count of LI nodes                 count                   Check to see if this node is the one passed in                 if  the li    node                                            If so  alert the current count                     alert count-1

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const nodes   Array prototype slice call  el parentNode childNodes        const index   nodes indexOf el       console log  index      index

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Another example just using a basic loop and index check  HTML   lt ul id  foo  gt       lt li gt 0 lt  li gt       lt li gt 1 lt  li gt       lt li gt 2 lt  li gt       lt li gt 3 lt  li gt       lt li gt 4 lt  li gt   lt  ul gt    JavaScript runs onload ready or after ul is rendered  var list   document getElementById  foo        items   list getElementsByTagName  li     list onclick   function e        var evt   e    window event      src   evt target    evt srcElement      var myIndex   findIndex src       alert myIndex       function findIndex  elem         var i  len   items length      for i 0  i lt len  i              if  items i    elem                return i                      return -1      Running Example  jsFiddle

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For just elements this can be used to find the index of an element amongst it s sibling elements   function getElIndex el        for  var i   0  el   el previousElementSibling  i         return i      Note that previousElementSibling isn t supported in IE lt 9

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You can use this to find the index of an element   Array prototype indexOf call yourUl  yourLi   This for example logs all indices   var lis   yourList getElementsByTagName  li    for var i   0  i  lt  lis length  i          console log Array prototype indexOf call lis  lis i          JSFIDDLE

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A modern native approach could make use of  Array from    - for example      x000D   x000D  const el   document getElementById  get-this-index   x000D  const index   Array from document querySelectorAll  li    indexOf el  x000D  document querySelector  h2   textContent    index     index   x000D   lt ul gt  x000D     lt li gt zero x000D     lt li gt one x000D     lt li id  get-this-index  gt two x000D     lt li gt three x000D   lt  ul gt  x000D   lt h2 gt  lt  h2 gt  x000D   x000D   x000D

[javascript] JavaScript DOM: Find Element Index In Container

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