What are the possible reasons for document.getElementById, $("#id") or any other DOM method / jQuery selector not finding the elements?

Example problems include:

jQuery silently failing to bind an event handler, and a standard DOM method returning null resulting in the error:

Uncaught TypeError: Cannot set property '...' of null

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Many questions are asked about why a certain DOM element is not found and the reason is often because the JavaScript code is placed before the DOM element. This is intended to be a canonical answer for these type of questions. It's community wiki, so please feel free to improve it. – Felix Kling

6 Answers 11

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The element you were trying to find wasn’t in the DOM when your script ran.

The position of your DOM-reliant script can have a profound effect upon its behavior. Browsers parse HTML documents from top to bottom. Elements are added to the DOM and scripts are (generally) executed as they're encountered. This means that order matters. Typically, scripts can't find elements which appear later in the markup because those elements have yet to be added to the DOM.

Consider the following markup; script #1 fails to find the <div> while script #2 succeeds:

<script>
  console.log("script #1: %o", document.getElementById("test")); // null
</script>
<div id="test">test div</div>
<script>
  console.log("script #2: %o", document.getElementById("test")); // <div id="test" ...
</script>

So, what should you do? You've got a few options:


Option 1: Move your script

Move your script further down the page, just before the closing body tag. Organized in this fashion, the rest of the document is parsed before your script is executed:

<body>
  <button id="test">click me</button>
  <script>
    document.getElementById("test").addEventListener("click", function() {
      console.log("clicked: %o", this);
    });
  </script>
</body><!-- closing body tag -->

Note: Placing scripts at the bottom is generally considered a best practice.


Option 2: jQuery's ready()

Defer your script until the DOM has been completely parsed, using ready():

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script>
  $(document).ready(function() {
    $("#test").click(function() {
      console.log("clicked: %o", this);
    });
  });
</script>
<button id="test">click me</button>

Note: You could simply bind to DOMContentLoaded or window.onload but each has its caveats. jQuery's ready() delivers a hybrid solution.


Option 3: Event Delegation

Delegated events have the advantage that they can process events from descendant elements that are added to the document at a later time.

When an element raises an event (provided that it's a bubbling event and nothing stops its propagation), each parent in that element's ancestry receives the event as well. That allows us to attach a handler to an existing element and sample events as they bubble up from its descendants... even those added after the handler is attached. All we have to do is check the event to see whether it was raised by the desired element and, if so, run our code.

jQuery's on() performs that logic for us. We simply provide an event name, a selector for the desired descendant, and an event handler:

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script>
  $(document).on("click", "#test", function(e) {
    console.log("clicked: %o",  this);
  });
</script>
<button id="test">click me</button>

Note: Typically, this pattern is reserved for elements which didn't exist at load-time or to avoid attaching a large amount of handlers. It's also worth pointing out that while I've attached a handler to document (for demonstrative purposes), you should select the nearest reliable ancestor.


Option 4: The defer attribute

Use the defer attribute of <script>.

[defer, a Boolean attribute,] is set to indicate to a browser that the script is meant to be executed after the document has been parsed.

<script src="https://gh-canon.github.io/misc-demos/log-test-click.js" defer></script>
<button id="test">click me</button>

For reference, here's the code from that external script:

document.getElementById("test").addEventListener("click", function(e){
   console.log("clicked: %o", this); 
});

Note: The defer attribute certainly seems like a magic bullet but it's important to be aware of the caveats...
1. defer can only be used for external scripts, i.e.: those having a src attribute.
2. be aware of browser support, i.e.: buggy implementation in IE < 10

Short and simple: Because the elements you are looking for do not exist in the document (yet).


For the remainder of this answer I will use getElementById as example, but the same applies to getElementsByTagName, querySelector and any other DOM method that selects elements.

Possible Reasons

There are two reasons why an element might not exist:

  1. An element with the passed ID really does not exist in the document. You should double check that the ID you pass to getElementById really matches an ID of an existing element in the (generated) HTML and that you have not misspelled the ID (IDs are case-sensitive!).

    Incidentally, in the majority of contemporary browsers, which implement querySelector() and querySelectorAll() methods, CSS-style notation is used to retrieve an element by its id, for example: document.querySelector('#elementID'), as opposed to the method by which an element is retrieved by its id under document.getElementById('elementID'); in the first the # character is essential, in the second it would lead to the element not being retrieved.

  2. The element does not exist at the moment you call getElementById.

The latter case is quite common. Browsers parse and process the HTML from top to bottom. That means that any call to a DOM element which occurs before that DOM element appears in the HTML, will fail.

Consider the following example:

<script>
    var element = document.getElementById('my_element');
</script>

<div id="my_element"></div>

The div appears after the script. At the moment the script is executed, the element does not exist yet and getElementById will return null.

jQuery

The same applies to all selectors with jQuery. jQuery won't find elements if you misspelled your selector or you are trying to select them before they actually exist.

An added twist is when jQuery is not found because you have loaded the script without protocol and are running from file system:

<script src="//somecdn.somewhere.com/jquery.min.js"></script>

this syntax is used to allow the script to load via HTTPS on a page with protocol https:// and to load the HTTP version on a page with protocol http://

It has the unfortunate side effect of attempting and failing to load file://somecdn.somewhere.com...


Solutions

Before you make a call to getElementById (or any DOM method for that matter), make sure the elements you want to access exist, i.e. the DOM is loaded.

This can be ensured by simply putting your JavaScript after the corresponding DOM element

<div id="my_element"></div>

<script>
    var element = document.getElementById('my_element');
</script>

in which case you can also put the code just before the closing body tag (</body>) (all DOM elements will be available at the time the script is executed).

Other solutions include listening to the load [MDN] or DOMContentLoaded [MDN] events. In these cases it does not matter where in the document you place the JavaScript code, you just have to remember to put all DOM processing code in the event handlers.

Example:

window.onload = function() {
    // process DOM elements here
};

// or

// does not work IE 8 and below
document.addEventListener('DOMContentLoaded', function() {
    // process DOM elements here
});

Please see the articles at quirksmode.org for more information regarding event handling and browser differences.

jQuery

First make sure that jQuery is loaded properly. Use the browser's developer tools to find out whether the jQuery file was found and correct the URL if it wasn't (e.g. add the http: or https: scheme at the beginning, adjust the path, etc.)

Listening to the load/DOMContentLoaded events is exactly what jQuery is doing with .ready() [docs]. All your jQuery code that affects DOM element should be inside that event handler.

In fact, the jQuery tutorial explicitly states:

As almost everything we do when using jQuery reads or manipulates the document object model (DOM), we need to make sure that we start adding events etc. as soon as the DOM is ready.

To do this, we register a ready event for the document.

$(document).ready(function() {
   // do stuff when DOM is ready
});

Alternatively you can also use the shorthand syntax:

$(function() {
    // do stuff when DOM is ready
});

Both are equivalent.

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Would it be worth amending the last bit about the ready event to reflect the "newer" preferred syntax, or is it better to leave it as-is so that it works across older versions? – Tieson T.
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For jQuery, is it worth also adding in the alternative $(window).load() (and possibly syntactic alternatives to the $(document).ready(), $(function(){})? It seems related, but it feels slightly tangential to the point you're making. – David Thomas
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@David: Good point with .load. Regarding syntax alternatives, they could be looked up in the documentation but since answers should be self contained, it might actually be worth adding them. Then again, I'm pretty sure this specific bit about jQuery was answered already and is probably covered in another answers and linking to it might suffice. – Felix Kling
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@David: I have to revise: Apparently .load is deprecated: api.jquery.com/load-event. I don't know if it's for images only or window as well. – Felix Kling
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Those are pretty much the reasons I didn't add those parts into the answer (despite the CW); but, as you say the 'answers should be self-contained.' Though if this is intended to become a/the canonical answer on the matter, it might still be worth adding? I'm...I dunno, I feel like I'm trying to push you into something that I'm not entirely sure of myself with these comments. Addenda: wow, I...honestly had no idea. Darn, I'll have to go do some reading, now... – David Thomas
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@David: No worries :) Even if you are not sure, it's good that you mentioned it. I will probably add just some simple code snippets to show the usage. Thanks for your input! – Felix Kling
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@FelixKling: I realize this is set up as a wiki, but before I go mucking up a good resource, what's you take on mentioning the quirks involved with jQuery Mobile: jquerymobile.com/demos/1.2.0/docs/api/globalconfig.html – Tieson T.
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The "does not exist" phrasing fails to account for elements that exist but are not in the document's node tree, having been either detached or not inserted in the first place. – Nathan Bubna
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@Nathan: Well, from a DOM methods point of view, elements that are not in the document don't exist. – Felix Kling
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@FelixKling document.createDocumentFragment() and node.removeChild(child) do not return "nonexistent" DOM nodes, and don't forget shadow DOM nodes, which are in the document, just not the query-able node tree. Point of view does not change the meaning of "exist", and such detached/shadow nodes are increasingly encountered as part of modern JavaScript development. There's no reason to stick with this outdated and potentially confusing phrasing. – Nathan Bubna
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Case two led to a devastating debugging session back when I first started doing JavaScript. – Jordan Gray
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The only thing I see missing is an expansion of: "Because the elements you are looking for do not exist." If you are manipulating the DOM after the page has loaded, then you need to make sure the new DOM elements you added are ready too. An example of this is the jQuery .load() method, which allows you to supply a "complete" callback function - providing utility similar to .ready(). – daalbert
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@daalbert: Do you think changing it to "do not exist in the document" would be better? – Felix Kling
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@FelixKling, I suppose I would say something like: "the elements you are looking for do not exist in the DOM when you try to access them." My point being that when you are dynamically loading content, it is possible some things won't be accessible (yet) when the window.onload event is fired. – daalbert

As @FelixKling pointed out, the most likely scenario is that the nodes you are looking for do not exist (yet).

However, modern development practices can often manipulate document elements outside of the document tree either with DocumentFragments or simply detaching/reattaching current elements directly. Such techniques may be used as part of JavaScript templating or to avoid excessive repaint/reflow operations while the elements in question are being heavily altered.

Similarly, the new "Shadow DOM" functionality being rolled out across modern browsers allows elements to be part of the document, but not query-able by document.getElementById and all of its sibling methods (querySelector, etc.). This is done to encapsulate functionality and specifically hide it.

Again, though, it is most likely that the element you are looking for simply is not (yet) in the document, and you should do as Felix suggests. However, you should also be aware that that is increasingly not the only reason that an element might be unfindable (either temporarily or permanently).

Reasons why id based selectors don't work

  1. element/DOM with id specified doesn't exist yet.
  2. element exist but is not registered in DOM [in case of HTML nodes appended dynamically from ajax responses]
  3. more than one elements with same id are present which is causing conflict.

solutions

  1. try to access element after its declaration or alternatively use stuff like $(document).ready();

  2. for elements coming from ajax responses, use .bind() method of jquery, older versions of jquery had .live() for the same.

  3. use tools [eg webdeveloper plugin for browsers] to find duplicate ids and remove them.

I just struggled with this. Sharing in case useful. Even when I used the debugger and found the items already existed at runtime, so there was no apparent reason why console logged (and fell over) with an undefined.

In the end I rewrote the line of code. I had not spelled it wrongly, but I think I'd capitalised the D of "ID". Now works great.

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If you misspelled the function name, then you should have seen a runtime error. – Felix Kling

If the element you are trying to access is inside an iframe and you try to access it outside the context of the iframe this will also cause it to fail.

If you want to get an element in an iframe you can find out how here.

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