Memory can now call a callback function when specific memory addresses have been written to.

chip/memory.js

     if (size > 0){
       this.__map = new Uint8Array(size);
     }
+    this.__listeners = {};
   }
 
   get size(){return (this.__map) ? this.__map.length : 0;}
 
   get byte(){return (this.__map) ? this.__map[this.__addr] : -1;}
   set byte(b){
-    if (!this.__ro && this.__map)
+    if (!this.__ro && this.__map){
       this.__map[this.__addr] = b;
+      if (this.__addr in this.__listeners)
+        this.__listeners[this.__addr].forEach((fn)=>{fn(b);});
+    }
+  }
+
+  onAddressWrite(addr, fn){
+    if (addr < 0 || addr >= this.size)
+      throw new RangeError("Memory address is out of bounds.");
+    if (typeof(fn) !== 'function')
+      throw new TypeErrpr("Expected a callback function.");
+    if (!(addr in this.__listeners))
+      this.__listeners[addr] = [];
+    // WARNING: Not testing to see if using the same function more than once.
+    this.__listeners[addr].push(fn);
   }
 
+  // This method is intended for the emulator to fill a Read-Only memory module with data prior to
+  // the start of execution. This method should never be used in a running system.
   sysStore(address, data){
     if (this.__map){
       let dc = data;