JavaScript获取选中文本的兼容写法

 
function getSelectedText() { //此函数代码源自：http://www.codetoad.com/javascript_get_selected_text.asp
var txt = "";
if (window.getSelection) {
txt = window.getSelection();
} else if (window.document.getSelection) {
txt = window.document.getSelection();
} else if (window.document.selection) {
txt = window.document.selection.createRange().text;
} 
return txt;
}