ajax的post用法

<button>点击之后,显示ajax返回的数据</button>

<script>
    window.onload=function(){
        var oBtn=document.getElementsByTagName(‘button‘)[0];
        oBtn.onclick=function(){
        var xmlhttp;
        if(window.XMLHttpRequest){
            xmlhttp=new XMLHttpRequest();
        }else{
            xmlhttp=new ActiveXObject("Microsoft XMLHTTP");
        }
        xmlhttp.onreadystatechange=function(){
            if(xmlhttp.readyState==4&&xmlhttp.status==200){
                oBtn.innerHTML=xmlhttp.responseText;
            }
        }
        xmlhttp.open(‘POST‘,‘index.php‘,true);
        xmlhttp.setRequestHeader(‘Content-Type‘,‘application/x-www-form-urlenconded‘);
        xmlhttp.send(‘text=我是响应文字‘);
}
    }
</script>    

<?php

    echo $_POST[‘text‘];