What would make offsetParent null?

问题

I am trying to do positioning in JavaScript. I am using a cumulative position function based on the classic quirksmode function that sums offsetTop and offsetLeft for each offsetParent until the top node.

However, I am running into an issue where the element I'm interested in has no offsetParent in Firefox. In IE offsetParent exists, but offsetTop and offsetLeft all sum up to 0, so it has the same problem in effect as in Firefox.

What would cause an element that is clearly visible and usable on the screen to not have an offsetParent? Or, more practically, how can I find the position of this element in order to place a drop-down beneath it?

Edit: Here's how to reproduce one particular instance of this (not solved by the currently-accepted answer):

Open the home page of Stack Overflow.

Run the following code in the Console of the web browser (e.g. Chromev21):

var e = document.querySelector('div');
console.log(e);
// <div id="notify-container"></div>
do{
  var s = getComputedStyle(e);
  console.log(e.tagName,s.display,s.visibility,s.position,e.offsetParent);
} while(e=e.parentElement)
// DIV block visible fixed null
// BODY block visible static null
// HTML block visible static null

Why is the offsetParent of that element null?

回答1:

If the document hasn't finished loading then offsetParent can be null

回答2:

I have made a test of 2,304 divs with unique combinations of values for position, display, and visibility, nested inside unique combinations of each of those values, and determined that:

an otherwise-valid element
that is a descendant of <body>
will not have an offsetParent value if:

The element has position:fixed (Webkit and IE9)
The element has display:none (Webkit and FF)
Any ancestor has display:none (Webkit and FF)

It is also reasonable to expect that an element that has no parent, or that is not added to the page itself (is not a descendant of the <body> of the page), will also have offsetParent==null.

回答3:

https://developer.mozilla.org/en/DOM/element.offsetParent

offsetParent returns null when the element has style.display set to "none".

回答4:

offsetParent will return null if your element object hasn't been appended to the DOM yet.

回答5:

This is an old question, but I have another case. If you manipulate the DOM, you may end up with a null offsetParent - in IE6 and IE7.

See: IE 6/7 - "Unspecified Error" when accessing offsetParent (Javascript)

回答6:

I have run into this problem when the sibling just to the left of the element is hidden:

<div id="parent">
  <div id="element1">some stuff</div>
  <div id="element2" style="display: none">some hidden stuff</div>
  <div id="element3">child whose offset we want</div>
</div>

I've run into the case where the offsetParent of element3 is null even though element3 itself is visible, and parent is visible.

I've seen thin is Firefox 3.6 and Chrome 5. It seems to also affect the getBoundingClientRect() function on the element3, which is really annoying since that works in so many other cases!

来源：https://stackoverflow.com/questions/306305/what-would-make-offsetparent-null

标签

javascript

html

positioning