How to find with javascript if element exists in DOM or it's virtual (has been just created by createElement)

Question

I'm looking for a way to find if element referenced in javascript has been inserted in the document.

Lets illustrate a case with following code:

var elem = document.createElement('div');

// Element has not been inserted in the document, i.e. not present

document.getElementByTagName('body')[0].appendChild(elem);

// Element can now be found in the DOM tree

Jquery has :visible selector, but it won't give accurate result when I need to find that invisible element has been placed somewhere in the document.

Answer 1

Here's an easier method that uses the standard Node.contains DOM API to check in an element is currently in the DOM:

document.body.contains(MY_ElEMENT);

CROSS-BROWSER NOTE: the document object in IE does not have a contains() method - to ensure cross-browser compatibility, use document.body.contains() instead. (or document.head.contains if you're checking for elements like link, script, etc)

 

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Notes on using a specific document reference vs Node-level ownerDocument:

Someone raised the idea of using MY_ELEMENT.ownerDocument.contains(MY_ELEMENT) to check for a node's presence in the document. While this can produce the intended result (albeit, with more verbosity than necessary in 99% of cases), it can also lead to unexpected results, depending on use-case. Let's talk about why:

If you are dealing with a node that currently resides in an separate document, like one generated with document.implementation.createHTMLDocument(), an <iframe> document, or an HTML Import document, and use the node's ownerDocument property to check for presence in what you think will be your main, visually rendered document, you will be in a world of hurt.

The node property ownerDocument is simply a pointer to whatever current document the node resides in. Almost every use-case of contains involves checking a specific document for a node's presence. You have 0 guarantee that ownerDocument is the same document you want to check - only you know that. The danger of ownerDocument is that someone may introduce any number of ways to reference, import, or generate nodes that reside in other documents. If they do so, and you have written your code to rely on ownerDocument's relative inference, your code may break. To ensure your code always produces expected results, you should only compare against the specifically referenced document you intend to check, not trust relative inferences like ownerDocument.

Answer 2

Do this:

var elem = document.createElement('div');
elem.setAttribute('id', 'my_new_div');

if (document.getElementById('my_new_div')) { } //element exists in the document.

Answer 3

The safest way is to test directly whether the element is contained in the document:

function isInDocument(el) {
    var html = document.body.parentNode;
    while (el) {
        if (el === html) {
            return true;
        }
        el = el.parentNode;
    }
    return false;
}

var elem = document.createElement('div');
alert(isInDocument(elem));
document.body.appendChild(elem);
alert(isInDocument(elem));