Web 前后端怎么交互

if (window.XMLHttpRequest) {

    //  IE7+, Firefox, Chrome, Opera, Safari 浏览器执行代码

    xmlhttp = new XMLHttpRequest();

} else {

    // IE6, IE5 浏览器执行代码

    xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");

}

xmlhttp.onreadystatechange = function(){

    if (xmlhttp.readyState == 4 && xmlhttp.status == 200)

    {

        alert(xmlhttp.responseText);

    }

}

xmlhttp.open("GET", "./get_user.php", true);

xmlhttp.send();

$.ajax({

    type: 'POST'

    url: './get_user.php',

    data: {uid: 123},

    dataType: 'json',

    success: function(result){

        console.log(result);

    }

});