Data transfer between PHP and JavaScript

In web development, communication between PHP and JavaScript is something that often needs to be done. Below is an example.

JavaScript side:

Be sure to set xmlHttp.setRequestHeader, otherwise the parameters passed to PHP will become null (line 43). Line 36 is the highlight.

<script type="text/javascript">
function GetJson() 
{
    var xmlHttp;
    try
    {
        // Firefox, Opera 8.0+, Safari
        xmlHttp = new XMLHttpRequest();
    }
    catch (e) 
    {
        // Internet Explorer
        try {
            xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
        }
        catch (e) 
        {
            try {
                xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
            }
            catch (e) {
                alert("您的浏览器不支持AJAX！");
                    return false;
            }
        }
    }
     
    xmlHttp.onreadystatechange = function() 
    {
        if (xmlHttp.readyState == 4) 
        {
            //alert(xmlHttp.responseText);
            var str = xmlHttp.responseText;
            document.getElementById(&#39;show&#39;).innerHTML +=str;
            //alert(str);
            var obj = eval(&#39;(&#39;+ xmlHttp.responseText +&#39;)&#39;);
            //var obj = eval(({"id":"123","name":"elar","age":"21"}));
            alert(obj.name);
        }
    }
    var data = "id=123";
    xmlHttp.open("POST", "testJson.php", true);
    xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded"); 
    xmlHttp.send("id=123");
}
</script>
<input type="button" onclick="GetJson()" value="按我！"/>
<hr />
<div id="show"></div>

PHP side [testJson.php]:

Note that the php file must be clean, and there must be no other tags outside the tag, otherwise the eval function cannot parse it.

<?php 
$res[&#39;id&#39;] = $_POST[&#39;id&#39;];
$res[&#39;name&#39;] = "elar";
$res[&#39;age&#39;] = "21";
$response = "hello this is response".$_POST[&#39;id&#39;];
echo json_encode($res);
?>

Summary:

js wants to send data to PHP, it uses xmlHttp.send("id=123");

PHP sends data to js, ​​it uses echo json_encode($res); (note The construction of variable $res should comply with JSON specifications)

js To parse the JSON format data sent by PHP, use var obj = eval('('+ xmlHttp.responseText +')');