Get position/offset of element relative to a parent container?

element.offsetLeft and element.offsetTop give an element's position with respect to its offsetParent (which is the nearest parent element with a position of relative or absolute.)

I got another Solution. Subtract parent property value from child property value

$('child-div').offset().top - $('parent-div').offset().top;

in pure js just use offsetLeft and offsetTop properties.
Example fiddle: http://jsfiddle.net/WKZ8P/

var elm = document.querySelector('span');
console.log(elm.offsetLeft, elm.offsetTop);

p   { position:relative; left:10px; top:85px; border:1px solid blue; }
span{ position:relative; left:30px; top:35px; border:1px solid red; }

<p>
    <span>paragraph</span>
</p>

I did it like this in Internet Explorer.

function getWindowRelativeOffset(parentWindow, elem) {
    var offset = {
        left : 0,
        top : 0
    };

    // relative to the target field's document
    offset.left = elem.getBoundingClientRect().left;
    offset.top = elem.getBoundingClientRect().top;

    // now we will calculate according to the current document, this current
    // document might be same as the document of target field or it may be
    // parent of the document of the target field
    var childWindow = elem.document.frames.window;
    while (childWindow != parentWindow) {
        offset.left = offset.left + childWindow.frameElement.getBoundingClientRect().left;
        offset.top = offset.top + childWindow.frameElement.getBoundingClientRect().top;
        childWindow = childWindow.parent;
    }

    return offset;
};

=================== you can call it like this

getWindowRelativeOffset(top, inputElement);

I focus on IE only as per my focus but similar things can be done for other browsers.