<textarea id="go"></textarea> 

html, body {
    margin: 0;
    padding: 0;
    width: 100%;
    height: 100%;
}
#go {
	width: 100%;
    height: 360px;
	background: yellow;
	border: none;
	margin: 0;
	padding: 0;
}

let go = document.getElementById("go");
let a = 3;
for (i = 0; i < a; i++) {
  go.innerHTML += i;
}