ajax -基础未封装-参数函数说明

1、Ajax 是 Asynchronous JavaScript and XML（以及 DHTML 等）的缩写
2、创建 XMLHttpRequest 对象，这是处理所有服务器通信的对象
	<script language="javascript" type="text/javascript">
		var xmlHttp = new XMLHttpRequest();
	</script>
3、  // Get the value of the "phone" field and stuff it in a variable called phone
	 var phone = document.getElementById("phone").value;
	 // Set some values on a form using an array called response
	 document.getElementById("order").value = response[0];
	 document.getElementById("address").value = response[1];

4、浏览器：在 Microsoft 浏览器上创建了一个 XMLHttpRequest。
	var xmlHttp = false;
	try {
	  xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
	} catch (e) {
	  try {
		xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
	  } catch (e2) {
		xmlHttp = false;
	  }
	}
5、以支持多种浏览器的方式创建 XMLHttpRequest 对象
	/* Create a new XMLHttpRequest object to talk to the Web server */
	var xmlHttp = false;
	/*@cc_on @*/
	/*@if (@_jscript_version >= 5)
	try {
	  xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
	} catch (e) {
	  try {
		xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
	  } catch (e2) {
		xmlHttp = false;
	  }
	}
	@end @*/
	if (!xmlHttp && typeof XMLHttpRequest != 'undefined') {
	  xmlHttp = new XMLHttpRequest();
	}
6、发出 Ajax 请求
	function callServer() {
	  // Get the city and state from the web form
	  var city = document.getElementById("city").value;
	  var state = document.getElementById("state").value;
	  // Only go on if there are values for both fields
	  if ((city == null) || (city == "")) return;
	  if ((state == null) || (state == "")) return;
	  // Build the URL to connect to
	  var url = "/scripts/getZipCode.php?city=" + escape(city) + "&state=" + escape(state);
	  // Open a connection to the server
	  xmlHttp.open("GET", url, true);
	  // Setup a function for the server to run when it's done
	  xmlHttp.onreadystatechange = updatePage;
	  // Send the request
	  xmlHttp.send(null);
	}
7、处理服务器响应
	function updatePage() {
	  if (xmlHttp.readyState == 4) {
		var response = xmlHttp.responseText;
		document.getElementById("zipCode").value = response;
	  }
	}