Clock can now handle 'layers'. Every added layer reduces call speed of grouped components by <hz>/<# layers>.

src/clock.js

 
 class Clock{
-  constructor(){
+  constructor(layers){
+    layers = (typeof(layers === 'number') && layers > 0) ?
+      Math.floor(layers) :
+      1;
     this.__ticktime = 1000;
-    this.__dt = 0;
-    this.__ltime = 0;
+    this.__dt = -1;
     this.__out = [];
+    this.__cl = 0;
+    for (let i=0; i < layers; i++)
+      this.__out.push([]);
   }
 
   get hz(){return Math.floor(1000 / this.__ticktime);}
   set hz(hz){
     if(hz >= 1){
       this.__ticktime = 1000 / hz;
-      this.__dt = 0;
-      this.__ltime = 0;
+      this.__dt = -1;
     }
   }
 
-  clk(fn){
+  get layers(){return this.__out.length;}
+
+  clk(fn, layer){
+    layer = (typeof(layer === 'number') && layer >= 0) ?
+      Math.floor(layer) :
+      0;
+    if (layer < 0 || layer >= this.__out.length)
+      throw new RangeError("Layer out of bounds.");
+
     if (typeof(fn) === 'function')
-      this.__out.push(fn);
+      this.__out[layer].push(fn);
     return this;
   }
 
-  tick(){
-    let ctime = (new Date()).getTime();
-    if(this.__ltime !== 0){
-      this.__dt += ctime - this.__ltime;
-      while(this.__dt > this.__ticktime){
-        this.__out.forEach((fn)=>{fn();});
-        this.__dt -= this.__ticktime
-      }
-    } else {
-      // Call all of the callbacks immediately. This is the first
-      // legit tick!
-      this.__out.forEach((fn)=>{fn();});
+  // NOTE: dt in milliseconds.
+  tick(dt){
+    let extraTick = false;
+    if (this.__dt < 0){
+      this.__dt = 0;
+      extraTick = true;
     }
-    this.__ltime = ctime;
+    let proc = (ddt) => {
+      this.__out[this.__cl].forEach((fn)=>{fn();});
+      if (ddt)
+        this.__dt -= this.__ticktime;
+      if (this.__out.length > 1)
+        this.__cl = (this.__cl === this.__out.length - 1) ? 0 : this.__cl + 1;
+    };
+
+
+    this.__dt += dt;
+    while(this.__dt > this.__ticktime)
+      proc(true);
+    if (extraTick)
+      proc(false);
+
     return this;
   }
 }