Get ID of element that called a function

Question

How can I get the ID of an element that called a JS function    body jpg is an image of a dog as the user points his her mouse around the screen at different parts of the body an enlarged image is shown  The ID of the area element is identical to the image filename minus the folder and extension    lt div gt       lt img src  images body jpg  usemap   anatomy   gt   lt  div gt    lt map name  anatomy  gt     lt area id  nose  shape  rect  coords  280 240 330 275  onmouseover  zoom     gt   lt  map gt    lt script type  text javascript  gt  function zoom      document getElementById  preview   src  images nose jpg      lt  script gt    lt div gt   lt img id  preview   gt   lt  div gt    I ve done my research and have come to Stack Overflow as a last resort  I m prefer a solution that doesn t involve jQuery

User · Answer

I know you don t want a jQuery solution but including javascript inside HTML is a big no no    I mean you can do it but there are lots of reasons why you shouldn t  read up on unobtrusive javascript if you want the details    So in the interest of other people who may see this question  here is the jQuery solution     document  ready function          area   mouseover function event            preview   attr  src    images       event srcElement  attr  id                 The major benefit is you don t mix javascript code with HTML  Further more  you only need to write this once and it will work for all  tags as opposed to having to specify the handler for each  separately   Additional benefit is that every jQuery handler receives an event object that contains a lot of useful data - such as the source of the event  type of the event and so on making it much easier to write the kind of code you are after   Finally since it s jQuery you don t need to think about cross-browser stuff - a major benefit especially when dealing with events

User · Answer

You can code the handler setup like this    lt area id  nose  shape  rect  coords  280 240 330 275  onmouseover  zoom call this    gt    Then this in your handler will refer to the element   Now  I ll offer the caveat that I m not 100  sure what happens when you ve got a handler in an  lt area gt  tag  largely because I haven t seen an  lt area gt  tag in like a decade or so   I think it should give you the image tag  but that could be wrong    edit  mdash  yes  it s wrong - you get the  lt area gt  tag  not the  lt img gt    So you ll have to get that element s parent  the map   and then find the image that s using it  that is  the  lt img gt  whose  usemap  attribute refers to the map s name    edit again  mdash  except it doesn t matter because you want the area s  id  durr   Sorry for not reading correctly

User · Answer

i also want this to happen    so just pass the id of the element in the called function and used in my js file     function copy i n     var range   document createRange    range selectNode document getElementById i    window getSelection   removeAllRanges    window getSelection   addRange range    document execCommand  copy    window getSelection   removeAllRanges    document getElementById n  value    Copied

User · Answer

You can use  this  in event handler   document getElementById  preview   onmouseover   function         alert this id       Or pass event object to handler as follows   document getElementById  preview   onmouseover   function evt        alert evt target id       It s recommended to use attachEvent for IE  lt  9  addEventListener IE9 and other browsers  to attach events  Example above is for brevity   function myHandler evt        alert evt target id      var el   document getElementById  preview    if  el addEventListener       el addEventListener  click   myHandler  false      else if  el attachEvent       el attachEvent  onclick   myHandler

User · Answer

Pass a reference to the element into the function when it is called    lt area id  nose  onmouseover  zoom this      gt    lt script gt    function zoom ele        var id   ele id       console log  area element id       id        lt  script gt

User · Answer

I m surprised that nobody has mentioned the use of this in the event handler   It works automatically in modern browsers and can be made to work in other browsers   If you use addEventListener or attachEvent to install your event handler  then you can make the value of this automatically be assigned to the object the created the event     Further  the user of programmatically installed event handlers allows you to separate javascript code from HTML which is often considered a good thing   Here s how you would do that in your code in plain javascript   Remove the onmouseover  zoom    from your HTML and install the event handler in your javascript like this      simplified utility function to register an event handler cross-browser function setEventHandler obj  name  fn        if  typeof obj     string             obj   document getElementById obj             if  obj addEventListener            return obj addEventListener name  fn          else if  obj attachEvent            return obj attachEvent  on    name  function    return fn call obj                 function zoom            you can use  this  here to refer to the object that caused the event        this here will refer to the calling object  which in this case is the  lt map gt       console log this id       document getElementById  preview   src  http   photos smugmug com photos 344290962 h6JjS-Ti jpg         register your event handler setEventHandler  nose    mouseover   zoom

User · Answer

For others unexpectedly getting the Window element  a common pitfall    lt a href  javascript myfunction this   gt click here lt  a gt    which actually scopes this to the Window object  Instead    lt a href  javascript nop    onclick  myfunction this   gt click here lt  a gt    passes the a object as expected   nop   is just any empty function

[javascript] Get ID of element that called a function

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