sidebar.ts: Extract multi-key shortcut command code

Make the multi-key command generic so that it works with other commands,
not just `\m`.

Use the array equality method from Abhi
(https://stackoverflow.com/users/2968762/abhi) on Stack Overflow:
https://stackoverflow.com/questions/7837456/how-to-compare-arrays-in-javascript/19746771#19746771

1 files changed, 29 insertions, 0 deletions

diff --git a/src/multi_key_command.ts b/src/multi_key_command.ts
new file mode 100644
index 0000000..7e303fe
--- /dev/null
+++ b/src/multi_key_command.ts
@@ -0,0 +1,29 @@
+import key_codes, { KeyCode } from './key_codes';
+
+export default function(
+	el: HTMLDocument | HTMLElement,
+	command: KeyCode[],
+	action: () => void
+): void {
+	var key_buffer: number[] = [];
+
+	el.addEventListener('keydown', function(e: KeyboardEvent) {
+		command.forEach((key_code) => {
+			if (e.keyCode === key_code) {
+				key_buffer.push(key_code);
+			}
+		});
+	});
+
+	el.addEventListener('keyup', function(e: KeyboardEvent) {
+		if (key_buffer.length >= 2) {
+			var command_executed = key_buffer.length === command.length
+				&& key_buffer.every((value, index) => value === command[index]);
+
+			if (command_executed) {
+				action();
+				key_buffer = [];
+			}
+		}
+	});
+};