ajax.html

<!DOCTYPE html>
<html lang="zh-cn">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #res{
            width: 200px;
            height: 100px;
            border: solid 1px #90b;
        }
    </style>
</head>
<body>
    <button>get</button>
    <div id="res">

    </div>
</body>
<script>
    let btn = document.getElementsByTagName('button')[0]
    let res = document.getElementById('res')
    btn.onclick = function(){
        // console.log('test');
        const xhr = new XMLHttpRequest()
        xhr.open('GET','http://127.0.0.1:3000/server')
        xhr.send();
        xhr.onreadystatechange = function(){
            if(xhr.readyState ===4){
                if(xhr.status ===200){
                    // console.log(xhr.status);
                    // console.log(xhr.statusText);
                    // console.log(xhr.response);
                    res.innerHTML = xhr.response
                }
            }
        }
    }
</script>
</html>