better editor features:

* statusbar with percent scrolled and `row:col` info
* current line highlights

playground/index.php

@@ -11,19 +11,44 @@
 			return elements.length < 2 ? elements[0] : elements;
 		};
 
-		const output  = $("#output");
-		const input   = $("#input");
-		const numbers = $(".linenumbers");
-		let timeout;
+		const output   = $("#output");
+		const input    = $("#input");
+		const numbers  = $(".linenumbers");
+		const position = $("#position");
+		const percent  = $("#percent");
+		const editor   = $(".editor");
+		let   lastLine = 1;
+		let   timeout;
+		let   lastSelection;
+
+		const onLineChange = event => {
+			const start = input.selectionStart;
+			if (start === lastSelection)
+				return;
+
+			const linesToCursor = input.value.substr(0, start).split("\n");
+			const currentLine   = linesToCursor.length;
+			const char          = linesToCursor[linesToCursor.length - 1].length;
+			const ll            = $(`#line_${lastLine}`);
+			if (ll)
+				ll.classList.remove("active");
+			$(`#line_${currentLine}`).classList.add("active");
+
+			position.innerHTML = `[${currentLine}:${char}]`;
+
+			lastLine = currentLine;
+			lastSelection = start;
+		}
 
 		const updateOutput = (event) => {
 			const text  = event ? event.target.value : input.value;
 			const lines = text.split("\n").length;
 			let   html  = "";
 			for (let i = 1; i <= lines; i++) {
-				html += `${i}<br>`;
+				html += `<span id="line_${i}">${i}</span>`;
 			}
 			numbers.innerHTML = html;
+			onLineChange();
 
 			timeout = setTimeout(() => {
 
@@ -40,6 +65,9 @@
 		document.addEventListener("DOMContentLoaded", () => {
 			updateOutput();
 
+			for (event of ["click", "change", "keydown", "focus"])
+				input.addEventListener(event, () => onLineChange());
+
 			input.addEventListener("keydown", event => {
 				if (event.key !== "Tab")
 					return;
@@ -56,6 +84,16 @@
 				clearTimeout(timeout);
 				updateOutput(event);
 			});
+
+			editor.addEventListener("scroll", () => {
+				const height = input.clientHeight - editor.clientHeight;
+				const top    = editor.scrollTop;
+				
+				const fromTop = Math.min(100, Math.max(0, Math.round(top * 100 / height)));
+				percent.innerHTML = `${fromTop}%`;
+
+				console.log("SCROOLLL", fromTop, height, top);
+			});
 		});
 
 		window.highlight = (col, row) => {
@@ -102,6 +140,7 @@
 		body {
 			display: grid;
 			grid-template-columns: 1fr 1fr;
+			grid-template-rows: auto 30px;
 			font-family: sans-serif;
 			margin: 0;
 			padding: 0;
@@ -146,28 +185,57 @@
 			height: 100%;
 			border-right: none;
 			overflow-y: auto;
+			border-bottom: none;
 			overflow-x: hidden;
 		}
 		
 		.linenumbers {
 			font-size: 1.2rem;
 			text-align: right;
-			padding: 1rem;
+			padding: 1rem 0;
 			color: #aaa;
 			font-family: monospace;
 			background: #222;
 		}
+		.linenumbers span {
+			display: block;
+			padding: 0 1rem;
+		}
+		.linenumbers span.active {
+			color: yellow;
+			background: rgba(255,255,255,0.05);
+		}
+
+		.statusbar {
+			font-size: 0.6rem;
+			line-height: 30px;
+			padding: 0 1rem;
+			background: rgba(0,0,0,0.2);
+			text-align: right;
+			border: none;
+			color: #888;
+		}
+
+		#position {
+			color: dodgerblue;
+			font-weight: bold;
+		}
 
 		#output {
 			overflow-y: auto;
 			padding: 4rem;
 			max-width: 100%;
+			grid-row: span 2;
 		}
 		#output code {
 			word-break: break-word;
 			white-space: break-spaces;
 		}
 
+		#output table {
+			width: 100%;
+		}
+
 		#output img {
 			max-width: 100%;
 			height: auto;
@@ -395,6 +463,10 @@ Unit tests can be run via `composer`:
 	</textarea>
 </section>
 <section id="output"></section>
+<section class="statusbar">
+	<span id="percent">0%</span>
+	<span id="position">[1:2]</span>
+</section>
 
 </body>
 </html>