First REPL mock

lib/commands.ts

@@ -0,0 +1,7 @@
+const commandList = ["about", "navigate", "external", "help", "ed", "nano"]
+
+export function commandCompletion(input: string): string {
+    if (input === "") return "";
+    const candidates = commandList.map((cmd) => [cmd.substring(0, input.length), cmd]).filter((cmd) => cmd[0] === input);
+    return candidates.length > 0 ? candidates[0][1] : "";
+}