Can multiple different HTML elements have the same ID if they re different elements

Question

Can multiple HTML elements have the same ID if they re of different element types  Is a scenario like this valid  Eg  div foo span foo a foo

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x000D   x000D   lt div id  one  gt first text for one lt  div gt  x000D   lt div id  one  gt second text for one lt  div gt  x000D   x000D  var ids   document getElementById  one    x000D   x000D   x000D    ids contain only first div element  So even if there are multiple elements with the same id  the document object will return only first match

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No   Element IDs should be unique within the entire document

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Can multiple elements have the same ID   Yes - whether they are the same tag or not  browsers will render the page even if multiple elements have the same ID   Is it Valid HTML   No  This is still true as of the HTML 5 1 spec  However  the spec also says getElementById must return the first element with the given ID  making the behavior not undefined in the case of an invalid document   What are the consequences of this type of invalid HTML   Most  if not all  browsers have selected and still do select the first element with a given ID  when calling getElementById   Most libraries that find elements by ID inherit this behavior   Most  if not all  browsers also apply styles assigned by id-selectors  e g   myid  to all elements with the specified ID   If this is what you expect and intend  then there are no unintended consequences   If you expect intend something else  e g  for all elements with that ID to be returned  or for the style to apply to only one element  then your expectations will not be met and any feature relying on those expectations will fail   Some javascript libraries do have expectations that are not met when multiple elements have the same ID  see wootscootinboogie s comment about d3 js   Conclusion  It s best to stick to the standards  but if you know your code works as expected in your current environments  and these IDs are used in a predictable maintainable way  then there are only 2 practical reasons not to do this    To avoid the chance that you are wrong  and one of the libraries you use actually does malfunction when multiple elements have the same ID  To maintain forward-compatibility of your website application with libraries or services  or developers   you may encounter in the future  that do malfunction when multiple elements have the same ID - which is a reasonable possibility since this is not  technically  valid HTML    The power is yours

User · Answer

I think you can t do it because Id is unique you have to use it for one element   You can use class for the purpose

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It s possible to have duplicate ids  I have tried adding the todoitem from javascript and it added to the dom successfully  This is the html code and javscript code

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Yes they can   I don t know if all these anwers are outdated  but just open youtube and inspect the html  Try to inspect the suggested videos  you ll see that they all have the same Id and repeating structure as follows    lt span id  video-title  class  style-scope ytd-compact-radio-renderer  title  Mix - LARA TACTICAL  gt

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And for what it s worth  on Chrome 26 0 1410 65  Firefox 19 0 2  and Safari 6 0 3 at least  if you have multiple elements with the same ID  jquery selectors  at least  will return the first element with that ID   e g    lt div id  one  gt first text for one lt  div gt   lt div id  one  gt second text for one lt  div gt    and  alert     one   size       See http   jsfiddle net RuysX  for a test

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How about a pragmatic answer  Let s go to youtube and run this code Object fromEntries Object entries     document querySelectorAll   id     reduce  s  e    gt    s e id     s e id     0    1  return s          filter   k v     gt  v  gt  1    and see all the repeated ids   Changing the code above to show ids repeated more than 10 times here s the list it produced additional-metadata-line  43 avatar  46 avatar-link  43 button  120 buttons  45 byline-container  45 channel-name  44 container  51 content  49 details  43 dismissable  46 dismissed  46 dismissed-content  43 hover-overlays  45 img  90 menu  50 meta  44 metadata  44 metadata-line  43 mouseover-overlay  45 overlays  45 repeat  36 separator  43 text  49 text-container  44 thumbnail  46 tooltip  80 top-level-buttons  45 video-title  43 video-title-link  43  Other sites that use the same id more than once include Amazon com  ebay com  expedia com  cnn com clearly ids are just another piece of metadata on an element  getElementById is pretty much obsolete  You can use querySelectorAll for all elements or querySelector for the first  regardless of selector so if you want all elements with id foo then document querySelectorAll   foo       returns all elements with id  quot foo quot   where as if you want only the first element use querySelector document querySelector   foo       returns the first element with id  quot foo quot  document querySelector   foo       returns the first element with class  quot foo quot  document querySelector  foo        returns the first  lt foo gt  element document querySelector  foo  foo  foo      returns the first element with                                            id  quot foo quot  that has an ancestor                                            with class  quot foo quot  who has an                                            ancestor  lt foo gt  element   And we can see that using selectors we can find different elements with the same id   x000D   x000D  function addClick selector  add      document querySelector selector  addEventListener  click   function         const e   this parentElement querySelector  span        e textContent   parseInt e textContent    add          addClick   e  foo   1   addClick   f  foo   10   x000D  body   font-size  x-large  font-weight  bold     a  foo   color  red     b  foo   color  green    div nth-child 3   foo   color  blue     foo   color  purple   x000D   lt div class  a  gt  lt span id  foo  gt a lt  span gt  lt  div gt   lt div class  b  gt  lt span id  foo  gt b lt  span gt  lt  div gt   lt div gt  lt span id  foo  gt c lt  span gt  lt  div gt   lt span id  foo  gt d lt  span gt   lt div class  e  gt  lt button type  button  id  foo  gt  1 lt  button gt    lt span gt 0 lt  span gt  lt  div gt   lt div class  f  gt  lt button type  button  id  foo  gt  10 lt  button gt    lt span gt 0 lt  span gt  lt  div gt  x000D   x000D   x000D   Where it matters that id is unique   lt a gt  tags can reference ids as in  lt a href  quot  foo quot  gt   Clicking it will jump the document to the first element with id  quot foo quot   Similarly the hash tag in the URL which is effectively the same feature    lt label gt  tags have a for attribute that specifies which element they are labeling by id  Clicking the label clicks activates give-the-focus-to the corresponding element  The label will only affect the first element with a matching id    x000D   x000D  label   user-select  none    x000D   lt p gt nested for checking lt  p gt   lt form gt     lt div gt  lt input type  checkbox  id  foo  gt  lt label for  foo  gt foo lt  label gt  lt  div gt   lt  form gt   lt form gt     lt div gt  lt input type  checkbox  id  foo  gt  lt label for  foo  gt foo  clicking here will check first checkbox  lt  label gt  lt  div gt   lt  form gt  x000D   x000D   x000D   Otherwise  id is just another tool in your toolbox

User · Answer

I think there is a difference between whether something SHOULD be unique or MUST be unique  i e  enforced by web browsers    Should IDs be unique  YES   Must IDs be unique  NO  at least IE and FireFox allow multiple elements to have the same ID

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The official spec for HTML states that id tags must be unique AND the official spec also states that if the render can be completed  it must  i e  there are no such thing as  errors  in HTML  only  invalid  HTML    So  the following is how id tags actually work in practice  They are all invalid  but still work   This    lt div id  unique  gt One lt  div gt   lt div id  unique  gt Two lt  div gt    Renders fine in all browsers   However  document getElementById only returns an object  not an array  you will only ever be able to select the first div via an id tag   If you were to change the id of the first div using JavaScript  the second ID would then be accessible with document getElementById  tested on Chrome  FireFox  amp  IE11    You can still select the div using other selection methods  and it s id property will be returned correctly   Please note this above issue opens a potential security vulnerability in sites that render SVG images  as SVGs are allowed to contain DOM elements  and also id tags on them  allows script DOM redirects via uploaded images   As long as the SVG is positioned in the DOM before the element it replaces  the image will receive all JavaScript events meant for the other element   This issue is currently not on anyone s radar as far as I know  yet it s real   This    lt div id  unique  id  unique-also  gt One lt  div gt    Also renders fine in all browsers   However  only the first id you define this way is utilized  if you tried document getElementById  unique-also    in the above example  you would be returned null  tested on Chrome  FireFox  amp  IE11    This    lt div id  unique unique-two  gt Two lt  div gt    Also renders fine in all browsers  however  unlike class tags that can be separated by a space  the id tag allows spaces  so the id of the above element is actually  unique unique-two   and asking the dom for  unique  or  unique-two  in isolation returns null unless otherwise defined elsewhere in the DOM  tested on Chrome  FireFox  amp  IE11

User · Answer

No   two elements with the same id are not valid   IDs are unique  if you wish to do something like that  use a class   Don t forget that elements can have multiple classes by using a space as a delimeter    lt div class  myclass sexy  gt  lt  div gt

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Well  using the HTML validator at w3 org  specific to HTML5  IDs must be unique  Consider the following      lt  DOCTYPE html gt    lt html gt       lt head gt           lt meta charset  UTF-8  gt           lt title gt MyTitle lt  title gt        lt  head gt       lt body gt           lt div id  x  gt Barry lt  div gt           lt div id  x  gt was lt  div gt           lt div id  x  gt here lt  div gt       lt  body gt   lt  html gt    the validator responds with      Line 9  Column 14  Duplicate ID x        lt div id  x  gt was lt  div gt  Warning Line 8  Column 14  The first occurrence of ID x was here         lt div id  x  gt Barry lt  div gt  Error Line 10  Column 14  Duplicate ID x         lt div id  x  gt here lt  div gt  Warning Line 8  Column 14  The first occurrence of ID x was here         lt div id  x  gt Barry lt  div gt        but the OP specifically stated - what about different element types   So consider the following HTML      lt  DOCTYPE html gt    lt html gt       lt head gt           lt meta charset  UTF-8  gt           lt title gt MyTitle lt  title gt        lt  head gt       lt body gt           lt div id  x  gt barry              lt span id  x  gt was here lt  span gt           lt  div gt       lt  body gt   lt  html gt        the result from the validator is     Line 9  Column 16  Duplicate ID x            lt span id  x  gt was here lt  span gt  Warning Line 8  Column 14  The first occurrence of ID x was here         lt div id  x  gt barry   Conclusion   In either case  same element type  or different element type   if the id is used more than once it is not considered valid HTML5

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Is it possible to have more than one student in a class having same Roll Id no  In HTMLid attribute is like so  You may use same class for them  e g    lt div class  a b c  gt  lt  div gt   lt div class  a b c d  gt  lt  div gt    And so on

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We can use class name instead of using id  html id are should be unique but classes are not  when retrieving data using class name can reduce number of code lines in your js files    x000D   x000D    document  ready function    x000D    x000D          class name   click function    x000D        x000D            code x000D          x000D      x000D   x000D   x000D

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SLaks answer is correct  but as an addendum note that the x html specs specify that all ids must be unique within a  single  html document  Although it s not exactly what the op asked  there could be valid instances where the same id is attached to different entities across multiple pages   Example    served to modern browsers  article main-content  styled one way     served to legacy  div main-content  styled another way   Probably an antipattern though  Just leaving here as a devil s advocate point

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Even if the elements are of different types it can cause you some serious problems     Suppose you have 3 buttons with the same id    lt button id  myid  data-mydata  this is button 1  gt button 1 lt  button gt   lt button id  myid  data-mydata  this is button 2  gt button 2 lt  button gt   lt button id  myid  data-mydata  this is button 3  gt button 3 lt  button gt    Now you setup some jQuery code to do something when myid buttons are clicked     document  ready function              myid   click function                  var buttonData     this  data  mydata                Call interesting function            interestingFunction                form   trigger  submit                  What would you expect  That every button clicked would execute the click event handler setup with jQuery  Unfortunately it won t happen  ONLY the 1st button calls the click handler  The other 2 when clicked do nothing  It is as if they weren t buttons at all   So always assign different IDs to HTML elements  This will get you covered against strange things       lt button id  button1  class  mybtn  data-mydata  this is button 1  gt button 1 lt  button gt   lt button id  button2  class  mybtn  data-mydata  this is button 2  gt button 2 lt  button gt   lt button id  button3  class  mybtn  data-mydata  this is button 3  gt button 3 lt  button gt    Now if you want the click event handler to run when any of the buttons get clicked it will work perfectly if you change the selector in the jQuery code to use the CSS class applied to them like this     document  ready function              mybtn   click function                  var buttonData     this  data  mydata                Call interesting function            interstingFunction                form   trigger  submit

User · Answer

Nope  IDs have to be unique  You can use classes for that purpose   lt div class  a    gt  lt div class  a b    gt  lt span class  a    gt   div a  font           or just      a  prop  value

[html] Can multiple different HTML elements have the same ID if they're different elements?

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