javascript与php使用json进行数据通信

<script>
/*
@desc 加载XHR文件
@author lee [<complet@163.com>]
@param file 文件路径
@param async 同步或异步 true 异步 flase 同步
@return xmlDoc 加载后的内容
*/
function loadDoc(file,async=true){
if(window.XMLHttpRequest){  // code for IE7+, Firefox, Chrome, Opera, Safari
    xmlhttp=new XMLHttpRequest();
}else{  // code for IE6, IE5
    xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
if(async === true){
    xmlhttp.onreadystatechange = function(){
        if(xmlhttp.readyState < 4){
            // 加载中
        }else if (xmlhttp.readyState == 4 && xmlhttp.status == 200){
            // 成功
            var xmlDoc
            if(xmlhttp.getResponseHeader('content-type')==='application/json'){
                xmlDoc = JSON.parse(xmlhttp.responseText);  
            }else{
                xmlDoc = xmlhttp.responseText
            }
            return xmlDoc
        }else{
            // 失败
            xmlhttp.abort()
            return
        }
    }
}
xmlhttp.open("POST",file,async);
xmlhttp.setRequestHeader("Content-type", "application/json");
var data = {name:"lee"}
var str = JSON.stringify(data)
xmlhttp.send(str);
if(async === false){
    var xmlDoc
    if(xmlhttp.getResponseHeader('content-type')==='application/json'){
        xmlDoc = JSON.parse(xmlhttp.responseText);  
    }else{
        xmlDoc = xmlhttp.responseText
    }
    return xmlDoc
}
}
var str = loadDoc('test.php',false)
console.log(str.name)
</script>

<?php
header("content-type:application/json");
$json = file_get_contents('php://input');
echo $json;