diff --git a/js/apple1io.js b/js/apple1io.js
deleted file mode 100644
index ab243f4..0000000
--- a/js/apple1io.js
+++ /dev/null
@@ -1,97 +0,0 @@
-/* Copyright 2010-2019 Will Scullin <scullin@scullinsteel.com>
- *
- * Permission to use, copy, modify, distribute, and sell this software and its
- * documentation for any purpose is hereby granted without fee, provided that
- * the above copyright notice appear in all copies and that both that
- * copyright notice and this permission notice appear in supporting
- * documentation.  No representations are made about the suitability of this
- * software for any purpose.  It is provided "as is" without express or
- * implied warranty.
- */
-
-export default function Apple1IO(text) {
-    var _key = 0;
-    var _keyReady = false;
-
-    var _displayReady = false;
-    var _nextDSP = 0;
-    var _buffer = [];
-
-    var LOC = {
-        KBD: 0x10,
-        KBDRDY: 0x011,
-        DSP: 0x12,
-        DSPCTL: 0x13
-    };
-
-    return {
-        start: function() { return 0xd0; },
-        end: function() { return 0xd0; },
-        read: function(page, off) {
-            var result = 0;
-            off &= 0x13;
-            switch (off) {
-            case LOC.KBD:
-                // Keyboard
-                if (_buffer.length) {
-                    result = _buffer.shift().toUpperCase().charCodeAt(0) & 0x7f;
-                    _keyReady = (_buffer.length > 0);
-                } else {
-                    result = _key;
-                    _keyReady = false;
-                }
-                result |= 0x80;
-                break;
-            case LOC.KBDRDY:
-                result = _keyReady ? 0x80 : 0x00;
-                break;
-            case LOC.DSP:
-                // Display
-                // result = (Math.random() > 0.5) ? 0x80 : 0x00;
-                result = (Date.now() > _nextDSP) ? 0x00 : 0x80;
-                break;
-            case LOC.DSPCTL:
-                break;
-            }
-            return result;
-        },
-        write: function(page, off, val) {
-            off &= 0x13;
-            switch (off) {
-            case LOC.KBD:
-                break;
-            case LOC.KBDRDY:
-                break;
-            case LOC.DSP:
-                // Display
-                if (_displayReady) {
-                    text.write(val);
-                }
-                _nextDSP = Date.now() + ((_buffer.length > 0) ? 0 : 17);
-                break;
-            case LOC.DSPCTL:
-                // Don't pretend we care what the value was...
-                _displayReady = true;
-                break;
-            }
-        },
-        reset: function apple1io_reset() {
-            text.clear();
-            _buffer = [];
-            _keyReady = false;
-            _displayReady = false;
-        },
-        keyUp: function apple1io_keyUp() {
-        },
-        keyDown: function apple1io_keyDown(key) {
-            _key = key;
-            _keyReady = true;
-        },
-        paste: function apple1io_paste(buffer) {
-            buffer = buffer.replace(/\/\/.*\n/g, '');
-            buffer = buffer.replace(/\n/g, '\r');
-            _buffer = buffer.split('');
-            _keyReady = true;
-        }
-    };
-}
diff --git a/js/apple1io.ts b/js/apple1io.ts
new file mode 100644
index 0000000..8e0a359
--- /dev/null
+++ b/js/apple1io.ts
@@ -0,0 +1,104 @@
+/* Copyright 2010-2023 Will Scullin <scullin@scullinsteel.com>
+ *
+ * Permission to use, copy, modify, distribute, and sell this software and its
+ * documentation for any purpose is hereby granted without fee, provided that
+ * the above copyright notice appear in all copies and that both that
+ * copyright notice and this permission notice appear in supporting
+ * documentation.  No representations are made about the suitability of this
+ * software for any purpose.  It is provided "as is" without express or
+ * implied warranty.
+ */
+
+import { TextPage } from "./canvas1";
+import type { byte } from "./types";
+
+const LOC = {
+  KBD: 0x10,
+  KBDRDY: 0x011,
+  DSP: 0x12,
+  DSPCTL: 0x13,
+} as const;
+
+export default class Apple1IO {
+  _key = 0;
+  _keyReady = false;
+
+  _displayReady = false;
+  _nextDSP = 0;
+  _buffer: string[] = [];
+
+  constructor(private text: TextPage) {}
+
+  start() {
+    return 0xd0;
+  }
+  end() {
+    return 0xd0;
+  }
+  read(_page: byte, off: byte): byte {
+    var result = 0;
+    off &= 0x13;
+    switch (off) {
+      case LOC.KBD:
+        // Keyboard
+        const key = this._buffer.shift();
+        if (key != null) {
+          result = key.toUpperCase().charCodeAt(0) & 0x7f;
+          this._keyReady = this._buffer.length > 0;
+        } else {
+          result = this._key;
+          this._keyReady = false;
+        }
+        result |= 0x80;
+        break;
+      case LOC.KBDRDY:
+        result = this._keyReady ? 0x80 : 0x00;
+        break;
+      case LOC.DSP:
+        // Display
+        // result = (Math.random() > 0.5) ? 0x80 : 0x00;
+        result = Date.now() > this._nextDSP ? 0x00 : 0x80;
+        break;
+      case LOC.DSPCTL:
+        break;
+    }
+    return result;
+  }
+  write(_page: byte, off: byte, val: byte): void {
+    off &= 0x13;
+    switch (off) {
+      case LOC.KBD:
+        break;
+      case LOC.KBDRDY:
+        break;
+      case LOC.DSP:
+        // Display
+        if (this._displayReady) {
+          this.text.write(val);
+        }
+        this._nextDSP = Date.now() + (this._buffer.length > 0 ? 0 : 17);
+        break;
+      case LOC.DSPCTL:
+        // Don't pretend we care what the value was...
+        this._displayReady = true;
+        break;
+    }
+  }
+  reset() {
+    this.text.clear();
+    this._buffer = [];
+    this._keyReady = false;
+    this._displayReady = false;
+  }
+  keyUp() {}
+  keyDown(key: byte) {
+    this._key = key;
+    this._keyReady = true;
+  }
+  paste(buffer: string) {
+    buffer = buffer.replace(/\/\/.*\n/g, "");
+    buffer = buffer.replace(/\n/g, "\r");
+    this._buffer = buffer.split("");
+    this._keyReady = true;
+  }
+}