prevent backspace key from leaving browser page

presets/apple2/tb_6502.s

@@ -3,7 +3,10 @@
 
 	.segment "INIT"
 	.segment "ONCE"
+; don't use $800-$1fff :(
 	.segment "STARTUP"
+        jmp Start
+; use $4000- :)
 	.segment "CODE"
 
 .define EQU =
@@ -146,7 +149,7 @@ PERFECT_AIM     EQU $1
   ;==============================
   ; back up part of the zero page
   ;==============================
-  
+Start:
 	lda	#>zero_page_save
 	sta	BASH
 	lda	#<zero_page_save
@@ -3029,7 +3032,7 @@ check_paddles:
 	LDY  #0        ;INIT COUNTER
 	NOP            ;COMPENSATE FOR 1ST COUNT
 	NOP
-PREAD2:	LDA  PADDL0,X  ;COUNT EVERY 11 µSEC.
+PREAD2:	LDA  PADDL0,X  ;COUNT EVERY 11 uSEC.
 	BPL  RTS2D     ;BRANCH WHEN TIMED OUT
 	INY            ;INCREMENT COUNTER
 	BNE  PREAD2    ;CONTINUE COUNTING

src/emu.ts

@@ -53,6 +53,9 @@ export enum KeyFlags {
 export function _setKeyboardEvents(canvas:HTMLElement, callback:KeyboardCallback) {
   canvas.onkeydown = (e) => {
     callback(e.which, 0, KeyFlags.KeyDown|_metakeyflags(e));
+    if (e.which == 8 || e.which == 9 || e.which == 27) { // eat backspace, tab, escape keys
+      e.preventDefault();
+    }
   };
   canvas.onkeyup = (e) => {
     callback(e.which, 0, KeyFlags.KeyUp|_metakeyflags(e));

src/machine/apple2.ts

@@ -243,7 +243,9 @@ export class AppleII extends BasicScanlineMachine {
     } else if (flags & KeyFlags.KeyDown) {
       code = 0;
       switch (key) {
+        case 8:  code=8; break; // left
         case 13: code=13; break; // return
+        case 27: code=27; break; // escape
         case 37: code=8; break; // left
         case 39: code=21; break; // right
         case 38: code=11; break; // up