get specific iframe with ID

iframe

function getFrameForDocument(document,id) {
    var w= document.defaultView || document.parentWindow;
    var frames= w.parent.document.getElementsByTagName('iframe');
    for (var i= frames.length; i-->0;) {
        var frame= frames[i];
        try {          
            if (frame.id===id)
               return frame.contentDocument || frame.contentWindow.document;
        } catch(e) {}
    }
}