small improvement to trigger examples in testprogram

testprogram.js

@@ -8,8 +8,16 @@
 //
 testprogramAddress=0x0000;
 
+// we want to auto-clear the console if any output is sent by the program
+var consoleboxStream="";
+
 // demonstrate write hook
-writeTriggers[0x000c]="consolebox.innerHTML = consolebox.innerHTML + String.fromCharCode(d);";
+writeTriggers[0x000c]="consoleboxStream += String.fromCharCode(d);"+
+                      "consolebox.innerHTML = consoleboxStream;";
+
+// demonstrate read hook (not used by this test program)
+readTriggers[0xD011]="((consolegetc==undefined)?0:0xff)";  // return zero until we have a char
+readTriggers[0xD010]="var c=consolegetc; consolegetc=undefined; (c)";
 
 testprogram = [
 	0xa9, 0x00,              // LDA #$00