第一个 XMLHttpRequest 例子（API）

【API】

https://developer.mozilla.org/zh-CN/docs/Web/API/XMLHttpRequest

【替代方案】

如果不想自己敲代码，可以直接访问以下URL测试代码。页面左侧是代码区，可修改（提交），右侧是实时结果。

http://www.w3school.com.cn/tiy/t.asp?f=xdom_httprequest_js_4

【代码准备】

如果想在本机试运行，往下看。

HTML代码：

<html>
<head>
<script type="text/javascript">
var xmlhttp;

function loadXMLDoc(url)
{
xmlhttp=null;
if (window.XMLHttpRequest)
  {// code for IE7, Firefox, Mozilla, etc.
  xmlhttp=new XMLHttpRequest();
  }
else if (window.ActiveXObject)
  {// code for IE5, IE6
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
if (xmlhttp!=null)
  {
  xmlhttp.onreadystatechange=onResponse;
  xmlhttp.open("GET",url,true);
  xmlhttp.send(null);
  }
else
  {
  alert("Your browser does not support XMLHTTP.");
  }
}

function onResponse()
{
if(xmlhttp.readyState!=4) return;
if(xmlhttp.status!=200)
  {
  alert("Problem retrieving XML data."+xmlhttp.statusText);
  return;
  }

txt="<table border='1'>";
x=xmlhttp.responseXML.documentElement.getElementsByTagName("CD");
for (i=0;i<x.length;i++)
  {
  txt=txt + "<tr>";
  xx=x[i].getElementsByTagName("TITLE");
    {
    try
      {
      txt=txt + "<td>" + xx[0].firstChild.nodeValue + "</td>";
      }
    catch (er)
      {
      txt=txt + "<td> </td>";
      }
    }
  xx=x[i].getElementsByTagName("ARTIST");
    {
    try
      {
      txt=txt + "<td>" + xx[0].firstChild.nodeValue + "</td>";
      }
    catch (er)
      {
      txt=txt + "<td> </td>";
      }
    }
  txt=txt + "</tr>";
  }
txt=txt + "</table>";
document.getElementById('copy').innerHTML=txt;

//----------------------------------------------------------------
resxml=xmlhttp.responseXML;

data1=resxml.documentURI;
data2=resxml.getElementsByTagName("CD").length;
data3=resxml.getElementsByTagName("CD")[0].getElementsByTagName("TITLE").length;
data4=resxml.getElementsByTagName("CD")[0].getElementsByTagName("TITLE")[0].firstChild.nodeValue;

document.getElementById('myoutput1').innerHTML=data1;
document.getElementById('myoutput2').innerHTML=data2;
document.getElementById('myoutput3').innerHTML=data3;
document.getElementById('myoutput4').innerHTML=data4;
//----------------------------------------------------------------
}
</script>
</head>

<body>
<p>documentURI----> <span id="myoutput1"></span></p>
<p>getElementsByTagName("CD").length----> <span id="myoutput2"></span></p>
<p>getElementsByTagName("TITLE").length----> <span id="myoutput3"></span></p>
<p>firstChild.nodeValue----><span id="myoutput4"></span></p>


<div id="copy">
<button onclick="loadXMLDoc('cd_catalog.xml')">Get CD info</button>
</div>
</body>
</html>

XML文件代码：

<?xml version="1.0"?>
<CATALOG>
  <CD>
    <TITLE>Empire Burlesque</TITLE>
    <ARTIST>Bob Dylan</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>Columbia</COMPANY>
    <PRICE>10.90</PRICE>
    <YEAR>1985</YEAR>
  </CD>
  <CD>
    <TITLE>Hide your heart</TITLE>
    <ARTIST>Bonnie Tyler</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>CBS Records</COMPANY>
    <PRICE>9.90</PRICE>
    <YEAR>1988</YEAR>
  </CD>
  <CD>
    <TITLE>Greatest Hits</TITLE>
    <ARTIST>Dolly Parton</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>RCA</COMPANY>
    <PRICE>9.90</PRICE>
    <YEAR>1982</YEAR>
  </CD>
  <CD>
    <TITLE>Still got the blues</TITLE>
    <ARTIST>Gary Moore</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>Virgin records</COMPANY>
    <PRICE>10.20</PRICE>
    <YEAR>1990</YEAR>
  </CD>
  <CD>
    <TITLE>Eros</TITLE>
    <ARTIST>Eros Ramazzotti</ARTIST>
    <COUNTRY>EU</COUNTRY>
    <COMPANY>BMG</COMPANY>
    <PRICE>9.90</PRICE>
    <YEAR>1997</YEAR>
  </CD>
  <CD>
    <TITLE>One night only</TITLE>
    <ARTIST>Bee Gees</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>Polydor</COMPANY>
    <PRICE>10.90</PRICE>
    <YEAR>1998</YEAR>
  </CD>
  <CD>
    <TITLE>Sylvias Mother</TITLE>
    <ARTIST>Dr.Hook</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>CBS</COMPANY>
    <PRICE>8.10</PRICE>
    <YEAR>1973</YEAR>
  </CD>
  <CD>
    <TITLE>Maggie May</TITLE>
    <ARTIST>Rod Stewart</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>Pickwick</COMPANY>
    <PRICE>8.50</PRICE>
    <YEAR>1990</YEAR>
  </CD>
  <CD>
    <TITLE>Romanza</TITLE>
    <ARTIST>Andrea Bocelli</ARTIST>
    <COUNTRY>EU</COUNTRY>
    <COMPANY>Polydor</COMPANY>
    <PRICE>10.80</PRICE>
    <YEAR>1996</YEAR>
  </CD>
  <CD>
    <TITLE>When a man loves a woman</TITLE>
    <ARTIST>Percy Sledge</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>Atlantic</COMPANY>
    <PRICE>8.70</PRICE>
    <YEAR>1987</YEAR>
  </CD>
  <CD>
    <TITLE>Black angel</TITLE>
    <ARTIST>Savage Rose</ARTIST>
    <COUNTRY>EU</COUNTRY>
    <COMPANY>Mega</COMPANY>
    <PRICE>10.90</PRICE>
    <YEAR>1995</YEAR>
  </CD>
  <CD>
    <TITLE>1999 Grammy Nominees</TITLE>
    <ARTIST>Many</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>Grammy</COMPANY>
    <PRICE>10.20</PRICE>
    <YEAR>1999</YEAR>
  </CD>
  <CD>
    <TITLE>For the good times</TITLE>
    <ARTIST>Kenny Rogers</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>Mucik Master</COMPANY>
    <PRICE>8.70</PRICE>
    <YEAR>1995</YEAR>
  </CD>
  <CD>
    <TITLE>Big Willie style</TITLE>
    <ARTIST>Will Smith</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>Columbia</COMPANY>
    <PRICE>9.90</PRICE>
    <YEAR>1997</YEAR>
  </CD>
  <CD>
    <TITLE>Tupelo Honey</TITLE>
    <ARTIST>Van Morrison</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>Polydor</COMPANY>
    <PRICE>8.20</PRICE>
    <YEAR>1971</YEAR>
  </CD>
  <CD>
    <TITLE>The very best of</TITLE>
    <ARTIST>Cat Stevens</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>Island</COMPANY>
    <PRICE>8.90</PRICE>
    <YEAR>1990</YEAR>
  </CD>
  <CD>
    <TITLE>Stop</TITLE>
    <ARTIST>Sam Brown</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>A and M</COMPANY>
    <PRICE>8.90</PRICE>
    <YEAR>1988</YEAR>
  </CD>
  <CD>
    <TITLE>Bridge of Spies</TITLE>
    <ARTIST>T'Pau</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>Siren</COMPANY>
    <PRICE>7.90</PRICE>
    <YEAR>1987</YEAR>
  </CD>
  <CD>
    <TITLE>Private Dancer</TITLE>
    <ARTIST>Tina Turner</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>Capitol</COMPANY>
    <PRICE>8.90</PRICE>
    <YEAR>1983</YEAR>
  </CD>
  <CD>
    <TITLE>Midt om natten</TITLE>
    <ARTIST>Kim Larsen</ARTIST>
    <COUNTRY>EU</COUNTRY>
    <COMPANY>Medley</COMPANY>
    <PRICE>7.80</PRICE>
    <YEAR>1983</YEAR>
  </CD>
  <CD>
    <TITLE>Pavarotti Gala Concert</TITLE>
    <ARTIST>Luciano Pavarotti</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>DECCA</COMPANY>
    <PRICE>9.90</PRICE>
    <YEAR>1991</YEAR>
  </CD>
  <CD>
    <TITLE>The dock of the bay</TITLE>
    <ARTIST>Otis Redding</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>Atlantic</COMPANY>
    <PRICE>7.90</PRICE>
    <YEAR>1987</YEAR>
  </CD>
  <CD>
    <TITLE>Picture book</TITLE>
    <ARTIST>Simply Red</ARTIST>
    <COUNTRY>EU</COUNTRY>
    <COMPANY>Elektra</COMPANY>
    <PRICE>7.20</PRICE>
    <YEAR>1985</YEAR>
  </CD>
  <CD>
    <TITLE>Red</TITLE>
    <ARTIST>The Communards</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>London</COMPANY>
    <PRICE>7.80</PRICE>
    <YEAR>1987</YEAR>
  </CD>
  <CD>
    <TITLE>Unchain my heart</TITLE>
    <ARTIST>Joe Cocker</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>EMI</COMPANY>
    <PRICE>8.20</PRICE>
    <YEAR>1987</YEAR>
  </CD>
</CATALOG>

View Code

【运行方法】

把2个文件放在同一级目录下。用浏览器打开HTML文件，按下按钮，读取XML文件。

运行结果：

【说明】

1、准备HTML页面

1.1、在html页面上创建一个Action，触发XMLHttpRequest实例化。
<button onclick="loadXMLDoc('cd_catalog.xml')">Get CD info</button>

1.2、在html页面上创建一个显示返回值的区域。
documentURI----> 
getElementsByTagName("CD").length----> 
getElementsByTagName("TITLE").length----> 
firstChild.nodeValue---->

2、省略各种错误处理，中心思想是创建XMLHttpRequest实例，并得到它的Response。
function loadXMLDoc(url)
{
xmlhttp=new XMLHttpRequest();
xmlhttp.onreadystatechange=onResponse;
xmlhttp.open("GET",url,true);
xmlhttp.send(null);
}

3、onreadystatechange是一个事件句柄。它的值 (state_onResponse) 是一个函数的名称。
通过responseXML属性的getElementsByTagName()方法得到各个节点的值。
function onResponse()
{
resxml=xmlhttp.responseXML;

data1=resxml.documentURI;
data2=resxml.getElementsByTagName("CD").length;
data3=resxml.getElementsByTagName("CD")[0].getElementsByTagName("TITLE").length;
data4=resxml.getElementsByTagName("CD")[0].getElementsByTagName("TITLE")[0].firstChild.nodeValue;

document.getElementById('myoutput1').innerHTML=data1;
document.getElementById('myoutput2').innerHTML=data2;
document.getElementById('myoutput3').innerHTML=data3;
document.getElementById('myoutput4').innerHTML=data4;
}
---------------------------------------------------------------------------------------------------------------
XMLHttpRequest的其他常用属性或方法：
document.getElementById("txtHint").innerHTML=任何值（Timing是onkeyup）
document.getElementById("myoutput").innerHTML=xmlhttp.status;
document.getElementById('p1').innerHTML=xmlhttp.getAllResponseHeaders();
document.getElementById('p1').innerHTML=xmlhttp.getResponseHeader('Last-Modified');
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