I made a console!

console.js

var jsconsole = (function() {
	var prompt = ">";
	var cursor = "_";
	var text = "";
	var cursor_displayed = true;
	var history = [];
	var history_cursor = -1;

	var jsconsole_div;
	var history_div;

	var jsconsole = { on_command: function (text) { console.log("butt"); } };
	jsconsole.prototype = Object.prototype;

	jsconsole.prototype.start = function() {
		jsconsole_div = document.querySelector("#line");
		history_div = document.querySelector("#history");

		jsconsole_div.innerHTML = prompt + text + cursor;
		setInterval(function() {
			old_html = jsconsole_div.innerHTML;
			if (cursor_displayed) {
				jsconsole_div.innerHTML = old_html.slice(0, old_html.length - 1);
			} else {
				jsconsole_div.innerHTML = old_html + cursor;
			}

			cursor_displayed = !cursor_displayed;
		}, 500);
	};

	jsconsole.prototype.keypress = function(event) {
		if (event.ctrlKey || event.altKey || event.metaKey)
			return;

		// Backspace and delete, respectively
		if (event.which == 8 || event.which == 46) {
			text = text.slice(0, text.length - 1);
		} else if (event.which == 13) {
			// Enter key

			if (cursor_displayed) {
				jsconsole_div.innerHTML = jsconsole_div.innerHTML.slice(0, jsconsole_div.innerHTML.length - 1);
			}

			if (history_div.innerHTML) {
				history_div.innerHTML += "<br />";
			}

			history_div.innerHTML += jsconsole_div.innerHTML;

			history.unshift(text);
			history_cursor = -1;
			if (!self.process_command(text) && text)
				jsconsole.on_command(text);

			text = "";
		} else if (event.keyCode == 38) {
			// Up arrow
			if (history_cursor + 1 < history.length) {
				text = history[++history_cursor];
			}
		} else if (event.keyCode == 40) {
			// Down arrow
			if (history_cursor > 0) {
				text = history[--history_cursor];
			} else if (history_cursor == 0) {
				text = "";
				history_cursor--;
			}
		} else if (event.keyCode == 9) {
			text = "\t" + text;
		} else {
			text += String.fromCharCode(event.which);		
		}

		jsconsole_div.innerHTML = prompt + text + cursor;
		cursor_displayed = true;
		window.scrollTo(0, document.body.scrollHeight);

		if (event.which == 8 || 
			event.which == 46 || 
			event.keyCode == 38 || 
			event.keyCode == 40 || 
			event.keyCode == 13 || 
			event.keyCode == 9)
				event.stopPropagation();
	};

	jsconsole.prototype.process_command = function(command) {
		if (command == ";clear") {
			history_div.innerHTML = "";
			return true;
		}

		return false;
	};

	return jsconsole;
})();

document.addEventListener("DOMContentLoaded", jsconsole.start);
document.addEventListener("keypress", jsconsole.keypress, true);