ajax工具方法

/*
 * 获取ajax对象
 */
function getXmlHttpRequest(){
    var xhr = null;
    if(typeof(XMLHttpRequest) != 'undefined'){
        xhr = new XMLHttpRequest();
    }else{
        xhr = new ActiveXObject("Microsoft.XMLHttp");
    }
    return xhr;
}

/*
 * post方式请求
 */
function post(url,queryString,fn){
    var xhr = getXmlHttpRequest();
    xhr.open('post',url,true);
    xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
    xhr.onreadystatechange=function(){
        if(xhr.readyState == 4){
            if(xhr.status == 200){
                fn.apply(this,[xhr]);
            }
        }
    };
    xhr.send(queryString);
}

/*
 * get方式请求
 */
function get(url,fn){
    var xhr = getXmlHttpRequest();
    xhr.open('get',true);
    xhr.onreadystatechange=function(){
        if(xhr.readyState == 4){
            if(xhr.status == 200){
                fn.apply(this,[xhr]);
            }
        }
    };
    xhr.send(null);
}

 /*
  * 测试
  */
post("ajax","",function(xhr){
    alert(xhr.responseText);
});

From :http://www.w3school.com.cn/xmldom/dom_http.asp