Renamed 6502 file to match exported class. Roughed out the class.

src/6502.js

-/*
- * Emulate a basic 6502 (MOS) chip.
- */
-
-// Registers
-var PC = 0;   // Program Counter (16 bit)
-var IRQ = 0;  // IRQ interrupt address code (16 bit)
-var SR = 0;   // Status Register (8 bit)
-var XR = 0;   // X Register (8 bit)
-var YR = 0;   // Y Register (8 bit)
-var AR = 0;   // Accumulator Register (8 bit)

src/MOS6502.js

+/*
+ * Emulate a basic 6502 (MOS) chip.
+ */
+
+var Memory = require('src/memory');
+
+class MOS6502{
+  constructor(){
+    // Registers
+    this.__PC = 0;   // Program Counter (16 bit)
+    this.__IRQ = 0;  // IRQ interrupt address code (16 bit)
+    this.__SR = 0;   // Status Register (8 bit)
+    this.__XR = 0;   // X Register (8 bit)
+    this.__YR = 0;   // Y Register (8 bit)
+    this.__AR = 0;   // Accumulator Register (8 bit)
+
+    // Variables to watch for Interrupts.
+    this.__nmi = false;
+    this.__irq = false;
+
+    // Memory module or controller.
+    this.__mem = null; // Must be explicitly attached.
+
+    // Hold any created CLK instances.
+    this.__clkfn = null;
+  }
+
+  set NMI(n){
+    this.__nmi = (n === true);
+  }
+
+  set IRQ(q){
+    // TODO: Verify this.
+    // TODO: Do not set if the interrupt flag is off.
+    this.__irq = (q === true);
+  }
+
+  CLK(){
+    if (this.__clkfn === null){
+      this.__clkfn = (function(){
+        // TODO: All the work!!
+      }).bind(this);
+    }
+    return this.__clkfn;
+  }
+
+  Memory(mem){
+    if (!(mem instanceof Memory))
+      throw new ValueError("Expected Memory instance object.");
+    this.__mem = mem;
+  }
+}
+
+
+module.exports = MOS6502;