AJAX之超時與網絡異常處理

<script>
        //獲取button
        const btn = document.getElementsByClassName("button")[0];
        console.log(btn)
        //綁定事件
        btn.addEventListener("click",function(){
            //創建對象
            const xhr = new XMLHttpRequest();

            //初始化對象
            xhr.open("POST","http://localhost:8000/ie?t="+Date.now());
            xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
            //設置請求頭
            xhr.setRequestHeader("name1","ddd");
            //發送
            xhr.send("a=3&b=4");
            //設置超時
            xhr.timeout=2000;
            //超時回調
            xhr.ontimeout=function(){
                alert("你的網絡超時了")
            }
            //網絡異常
            xhr.onerror=function(){
                alert("你斷網了")
            }
            //事件綁定
            xhr.onreadystatechange=function(){
                //判斷響應
                if( xhr.readyState ===4 ){
                    if(xhr.status >=200 && xhr.status <300){
                        div.innerHTML=xhr.response;
                    }    
                }
            }
        })

    </script>