how i get channel banner using youtube api in javascript?

i am using this code please help me to get channel banner?

Live Sub Counter

<span id="channel_name"></span>
<span id="sub_count"></span>

function result(channel_id)
{
if (channel_id === "")
{
return alert("Please enter a Channel ID");
}
document.getElementById("channel_id").value = "";

//for the request
request_data(channel_id);

}

function request_data(channel_id)
{
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function()
{
if (this.readyState == 4 && this.status == 200)
{
var output = this.responseText;
output = JSON.parse(output);
document.getElementById("channel_name").innerHTML = output.items[0].snippet["title"];
document.getElementById("sub_count").style.display = "inline";
if(output.items[0].statistics["hiddenSubscriberCount"] === true)
{
console.log("Subscriber count is hidden by the channel");
return document.getElementById("sub_count").innerHTML = "N/A";
}
document.getElementById("sub_count").innerHTML = output.items[0].statistics["subscriberCount"];
}
else if(this.readyState == 4)
{
return console.log(JSON.parse(this.responseText)["error"]["message"]);
}
};
xhttp.open("GET", "https://www.googleapis.com/youtube/v3/channels?part=snippet,statistics&id="+channel_id+"&key=AIzaSyDxF-lYhQOFbcA1qd22DMbmgoVRFzAE3hQ", true);
xhttp.send();
setTimeout(request_data, 2500);
}