List all letters used on a page.

list-letters.js

var text = document.body.innerText;
var letters = '';
var i = 0;
while ( i < text.length ) {
	var isithere = letters.split(text[i]);
	if (isithere.length == 1) {
		letters += text[i];
	}
	i++;
}
var textarea = document.createElement('textarea');
textarea.innerHTML = letters;
textarea.setAttribute('style','position:fixed;top:5vh;left:5vw;height:90vh;width:90vw;box-shadow:0 0 5vmax black;background:white');
document.body.appendChild(textarea);