RAM, ROM, and Shadow memory now use the new IO class. Dropped the Listener helper class.

src/memory/memory.js

 
-var IMem = require('./imem');
+const IO = require('../common/io.js');
+const IMem = require('./imem');
 
-class Listener{
-  constructor(){
-    this.__listeners = {};
-  }
-
-  on(n, fn){
-    if (typeof(fn) !== 'function')
-      throw new TypeErrpr("Expected a callback function.");
-    if (!(n in this.__listeners))
-      this.__listeners[n] = [];
-    this.__listeners[n].push(fn);
-  }
-
-  trigger(n, data){
-    if (n in this.__listeners){
-      this.__listeners[n].forEach((l)=>{
-        l(data);
-      });
-    }
-  }
-}
 
 class ROM extends IMem{
   constructor(pages){
     super();
     this.__addr = 0;
     this.__map = new Uint8Array(pages * 256);
-    this.__rlisteners = new Listener();
+    // Allow writable events because RAM will inherit ROM and use the same
+    // __io object.
+    this.__io = new IO([], []);
   }
 
   get pages(){return this.__map.length / 256;}
   }
 
   get byte(){
-    this.__rlisteners.trigger(this.__addr);
+    this.__io.triggerRead(this.__addr);
     return this.__map[this.__addr];
   }
   set byte(b){}
   onAddressRead(addr, fn){
     if (addr < 0 || addr >= this.size)
       throw new RangeError("Memory address is out of bounds."); 
-    this.__rlisteners.on(addr, fn);
+    this.__io.onRead(addr, fn);
     return this;
   }
 
 class RAM extends ROM {
   constructor(pages){
     super(pages);
-    this.__wlisteners = new Listener();
   }
 
   get pages(){return this.__map.length/256;}
   }  
 
   get byte(){
-    this.__rlisteners.trigger(this.__addr);
+    this.__io.triggerRead(this.__addr);
     return this.__map[this.__addr];
   }
   set byte(b){
     this.__map[this.__addr] = b & 0xFF;
-    this.__wlisteners.trigger(this.__addr, b & 0xFF);
+    this.__io.triggerWrite(this.__addr, b & 0xFF);
   }
 
   onAddressWrite(addr, fn){
     if (addr < 0 || addr >= this.size)
       throw new RangeError("Memory address is out of bounds.");
-    this.__wlisteners.on(addr, fn);
+    this.__io.onWrite(addr, fn);
     return this;
   }
 
     this.__addr = 0;
     this.__size = pages * 256;
 
-    this.__rlisteners = new Listener();
-    this.__wlisteners = new Listener();
+    this.__io = new IO([], []);
   }
 
   get pages(){return this.__size/256;}
 
   get byte(){
     let a = this.__addr % this.__map.length;
-    this.__rlisteners.trigger(this.__addr);
+    this.__io.triggerRead(this.__addr);
     return this.__map[a];
   }
   set byte(b){
     if (this.__addr >= 0 && this.__addr < this.__map.length){
       this.__map[this.__addr] = b & 0xFF;
-      this.__wlisteners.trigger(this.__addr, b & 0xFF);
+      this.__io.triggerWrite(this.__addr, b & 0xFF);
     }
   }
 
   onAddressRead(addr, fn){
     if (addr < 0 || addr >= this.size)
       throw new RangeError("Memory address is out of bounds."); 
-    this.__rlisteners.on(addr, fn);
+    this.__io.onRead(addr, fn);
     return this;
   }
 
     if (addr < 0 || addr >= this.size)
       throw new RangeError("Memory address is out of bounds.");
     let a = this.__addr % this.__map.length;
-    this.__wlisteners.on(a, fn);
+    this.__io.onWrite(a, fn);
     return this;
   }