Retrieve the position (X,Y) of an HTML element

The libraries go to some lengths to get accurate offsets for an element.
here's a simple function that does the job in every circumstances that I've tried.

function getOffset( el ) {
    var _x = 0;
    var _y = 0;
    while( el && !isNaN( el.offsetLeft ) && !isNaN( el.offsetTop ) ) {
        _x += el.offsetLeft - el.scrollLeft;
        _y += el.offsetTop - el.scrollTop;
        el = el.offsetParent;
    }
    return { top: _y, left: _x };
}
var x = getOffset( document.getElementById('yourElId') ).left; 

If you want it done only in javascript, here are some one liners using getBoundingClientRect()

window.scrollY + document.querySelector('#elementId').getBoundingClientRect().top // Y

window.scrollX + document.querySelector('#elementId').getBoundingClientRect().left // X

The first line will return offsetTop say Y relative to document. The second line will return offsetLeft say X relative to document.

getBoundingClientRect() is a javascript function that returns the position of the element relative to viewport of window.

HTML elements on most browsers will have:-

offsetLeft
offsetTop

These specifiy the position of the element relative its nearest parent that has layout. This parent can often be accessed bif the offsetParent property.

IE and FF3 have

clientLeft
clientTop

These properties are less common, they specify an elements position with its parents client area (padded area is part of the client area but border and margin is not).

Here's a modern 1-liner using vanilla JS to recursively iterate over element.offsetTop and element.offsetParent:

Function:

getTop = el => el.offsetTop + (el.offsetParent && getTop(el.offsetParent))

Usage:

const el = document.querySelector('#div_id');
const elTop = getTop(el)

Advantage:

Always returns the absolute vertical offset, regardless of the current scroll position.

Traditional syntax:

function getTop(el) {
  return el.offsetTop + (el.offsetParent && getTop(el.offsetParent));
}

You might be better served by using a JavaScript framework, that has functions to return such information (and so much more!) in a browser-independant fashion. Here are a few:

• Prototype
• jQuery
• MooTools
• YUI (yahoo)

With these frameworks, you could do something like: $('id-of-img').top to get the y-pixel coordinate of the image.

Update:

The recursion approach (in my old answer) creates many call stacks. We can use a while loop to avoid recursion in this case:

/**
 *
 * @param {HTMLElement} el
 * @return {{top: number, left: number}}
 */
function getDocumentOffsetPosition(el) {
    let top = 0, left = 0;
    while (el !== null) {
        top += el.offsetTop;
        left += el.offsetLeft;
        el = el.offsetParent;
    }
    return {top, left};
}

Old answer:

/**
 *
 * @param {HTMLElement} el
 * @return {{top: number, left: number}}
 */
function getDocumentOffsetPosition(el) {
    var position = {
        top: el.offsetTop,
        left: el.offsetLeft
    };
    if (el.offsetParent) {
        var parentPosition = getDocumentOffsetPosition(el.offsetParent);
        position.top += parentPosition.top;
        position.left += parentPosition.left;
    }
    return position;
}

Thank ThinkingStiff for the answer, this is only another version.

if using jQuery, the dimensions plugin is excellent and allows you specify exactly what you want.

e.g.

Relative position, absolute position, absolute position without padding, with padding...

It goes on, let's just say there is a lot you can do with it.

Plus the bonus of using jQuery is it's lightweight file size and easy use, you won't go back to JavaScript without it afterwards.

To get the total offset of an element, you could recursively sum up all parent offsets:

function getParentOffset(el): number {
if (el.offsetParent) {
    return el.offsetParent.offsetTop + getParentOffset(el.offsetParent);
} else {
    return 0;
}
}

with this utility function the total top offset of a dom element is:

el.offsetTop + getParentOffset(el);

While this is very likely to be lost at the bottom of so many answers, the top solutions here were not working for me.
As far as I could tell neither would any of the other answers have helped.

Situation:
In an HTML5 page I had a menu that was a nav element inside a header (not THE header but a header in another element).
I wanted the navigation to stick to the top once a user scrolled to it, but previous to this the header was absolute positioned (so I could have it overlay something else slightly).
The solutions above never triggered a change because .offsetTop was not going to change as this was an absolute positioned element. Additionally the .scrollTop property was simply the top of the top most element... that is to say 0 and always would be 0.
Any tests I performed utilizing these two (and same with getBoundingClientRect results) would not tell me if the top of the navigation bar ever scrolled to the top of the viewable page (again, as reported in console, they simply stayed the same numbers while scrolling occurred).

Solution
The solution for me was utilizing

window.visualViewport.pageTop

The value of the pageTop property reflects the viewable section of the screen, therefore allowing me to track where an element is in reference to the boundaries of the viewable area.

Probably unnecessary to say, anytime I am dealing with scrolling I expect to use this solution to programatically respond to movement of elements being scrolled.
Hope it helps someone else.
IMPORTANT NOTE: This appears to work in Chrome and Opera currently & definitely not in Firefox (6-2018)... until Firefox supports visualViewport I recommend NOT using this method, (and I hope they do soon... it makes a lot more sense than the rest).


UPDATE:
Just a note regarding this solution.
While I still find what I discovered to be very valuable for situations in which "...programmatically respond to movement of elements being scrolled." is applicable. The better solution for the problem that I had was to use CSS to set position: sticky on the element. Using sticky you can have an element stay at the top without using javascript (NOTE: there are times this will not work as effectively as changing the element to fixed but for most uses the sticky approach will likely be superior)

UPDATE01:
So I realized that for a different page I had a requirement where I needed to detect the position of an element in a mildly complex scrolling setup (parallax plus elements that scroll past as part of a message). I realized in that scenario that the following provided the value I utilized to determine when to do something:

  let bodyElement = document.getElementsByTagName('body')[0];
  let elementToTrack = bodyElement.querySelector('.trackme');
  trackedObjPos = elementToTrack.getBoundingClientRect().top;
  if(trackedObjPos > 264)
  {
    bodyElement.style.cssText = '';
  }

Hope this answer is more widely useful now.

This is easy as two lines in JS :

var elem = document.getElementById("id");    
alert(elem.getBoundingClientRect());