Html 取得鼠标选择的文本

function _getSelectedText() {
            if (window.getSelection) {
                var sel = window.getSelection();
                if (sel.rangeCount > 0) {
                    var range = sel.getRangeAt(0);
                    return range;
                }
            } else {
                var range = document.selection.createRange();
                    return range.text;
                }
            }
            return "";
        }