Coordinates of selected text in browser page

In IE >= 9 and non-IE browsers (Firefox 4+, WebKit browsers released since early 2009, Opera 11, maybe earlier), you can use the getClientRects() method of Range. In IE 4 – 10, you can use the boundingLeft and boundingTop properties of the TextRange that can be extracted from the selection. Here’s a function that will do what you want in recent browsers.

Note that there are some situations in which you may wrongly get co-ordinates 0, 0, as mentioned in the comments by @Louis. In that case you’ll have to fall back to a workaround of temporarily inserting an element and getting its position.

jsFiddle: http://jsfiddle.net/NFJ9r/132/

Code:

function getSelectionCoords(win) {
    win = win || window;
    var doc = win.document;
    var sel = doc.selection, range, rects, rect;
    var x = 0, y = 0;
    if (sel) {
        if (sel.type != "Control") {
            range = sel.createRange();
            range.collapse(true);
            x = range.boundingLeft;
            y = range.boundingTop;
        }
    } else if (win.getSelection) {
        sel = win.getSelection();
        if (sel.rangeCount) {
            range = sel.getRangeAt(0).cloneRange();
            if (range.getClientRects) {
                range.collapse(true);
                rects = range.getClientRects();
                if (rects.length > 0) {
                    rect = rects[0];
                }
                x = rect.left;
                y = rect.top;
            }
            // Fall back to inserting a temporary element
            if (x == 0 && y == 0) {
                var span = doc.createElement("span");
                if (span.getClientRects) {
                    // Ensure span has dimensions and position by
                    // adding a zero-width space character
                    span.appendChild( doc.createTextNode("\u200b") );
                    range.insertNode(span);
                    rect = span.getClientRects()[0];
                    x = rect.left;
                    y = rect.top;
                    var spanParent = span.parentNode;
                    spanParent.removeChild(span);

                    // Glue any broken text nodes back together
                    spanParent.normalize();
                }
            }
        }
    }
    return { x: x, y: y };
}

UPDATE

I submitted a WebKit bug as a result of the comments, and it’s now been fixed.

https://bugs.webkit.org/show_bug.cgi?id=65324