原生JS获取接口

一进入页面就触发接口

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8" />
        <title></title>
    </head>
    <body>
        <div class="btn"></div>
        <div class="message">跳转页面</div>
        <script>
            var btn=document.querySelector(".btn")
            var xhr=new XMLHttpRequest();
            xhr.onreadystatechange=function(){
              if(xhr.readyState==4&&xhr.status==200){
                   showMessage(JSON.parse(xhr.responseText));
                }
                }
                xhr.open('get',"接口",true);
                xhr.send();
            function showMessage(data){
                for(var i=0;i<data.length;i++){
                    message.innerHTML+=data[i]+'<br>';
                }
            }
        </script>
    </body>
</html>
    var ChipUuid = ''
    var GsmModuleNumid = ''
    var phone = ''
    var xhr=new XMLHttpRequest();
    xhr.onreadystatechange=function(){
       if(xhr.readyState==4&&xhr.status==200){
            ChipUuid = JSON.parse(xhr.responseText).data.ChipUuid
            GsmModuleNumid = JSON.parse(xhr.responseText).data.GsmModuleNumid
            phone = JSON.parse(xhr.responseText).data.phone
            console.log(phone)
                    }
                }
      xhr.open('get',"接口",true);
      xhr.send();