最近看JavaScript高級程序設計，大有收獲，接下來幾天寫一下讀書筆記。之前寫了一篇Ajax初步理解的隨筆，里面有個函數用來創建XmlHttpRequest對象,瀏覽器兼容性原因，寫出的代碼通過大量if判斷或者try，catch語句將函數引導到正確代碼處。

復制代碼 代碼如下:

<script type="text/javascript">
function createXHR(){
var xhr = null;
try {
// Firefox, Opera 8.0+, Safari，IE7+
xhr = new XMLHttpRequest();
}
catch (e) {
// Internet Explorer
try {
xhr = new ActiveXObject("Msxml2.XMLHTTP");
}
catch (e) {
try {
xhr = new ActiveXObject("Microsoft.XMLHTTP");
}
catch (e) {
xhr = null;
}
}
}
return xhr;
}
</script>

復制代碼 代碼如下:

function createXHR(){
var xhr=null;
if(typeof XMLHttpRequest !='undefined'){
xhr = new XMLHttpRequest();
createXHR=function(){
return new XMLHttpRequest();
}
}else{
try {
xhr = new ActiveXObject("Msxml2.XMLHTTP");
createXHR=function(){
return new ActiveXObject("Msxml2.XMLHTTP");
}
}
catch (e) {
try {
xhr = new ActiveXObject("Microsoft.XMLHTTP");
createXHR=function(){
return new ActiveXObject("Microsoft.XMLHTTP");
}
}
catch (e) {
createXHR=function(){
return null;
}
}
}
}
return xhr;
}