Get HTMLElement offset relative to offsetParent, minus transforms

getOffsetFromParent.js

function getOffset (node) {
    var doc = node.ownerDocument;
    var docElem = doc.documentElement;
    var win = doc.defaultView;
    var rect;
    var result;
    try {
        rect = node.getBoundingClientRect();
    } catch (e) {
        return { left: 0, top: 0 };
    }
    var matrixString = window.getComputedStyle(node).transform; // can be "none"
    var matrix = getCSSMatrix(matrixString);
    result = {
        left: rect.left + win.pageXOffset - docElem.clientLeft,
        top: rect.top + win.pageYOffset - docElem.clientTop
    };
    if (matrix.length) {
        result.left -= matrix[4];
        result.top -= matrix[5];
    }
    return result;
}

function getCSSMatrix (computedStyle) {
    var values = computedStyle.split(/\w+\(|\);?/);
    if (!values[1] || !values[1].length) {
        return [];
    }
    return values[1].split(/,\s?/g).map(function (str) { return parseInt(str, 10) });
}