function getSelectedText() {
    //document.designMode = 'on';
    var userSelection, ta;
    if (window.getSelection && document.activeElement){
        if (document.activeElement.nodeName == "TEXTAREA" || (document.activeElement.nodeName == "INPUT" &&
        document.activeElement.getAttribute("type").toLowerCase() == "text")){
            ta = document.activeElement;
            userSelection = ta.value.substring(ta.selectionStart,ta.selectionEnd);
        } else {
            userSelection = window.getSelection().getRangeAt(0);
        }
        return userSelection.toString();
    } else {
        //all browsers, except IE before version 9
        if (document.getSelection){
            userSelection = document.getSelection().getRangeAt(0);
            return userSelection.toString();
        }
        // IE below version 9
        else if (document.selection){
            userSelection = document.selection.createRange();
            return userSelection.text;
        }
    }
    return "";
}

上面是我获取的函数，但是经过实验发现，可以得到 userSelection 对象，但是通过 toString 得到的文本却是空，请大家帮帮忙，多谢！！！

我的环境：ubuntu+chrome