diff --git a/prosperon/examples/chess/grid.cm b/prosperon/examples/chess/grid.cm
index 868f90a7..c6cdffa4 100644
--- a/prosperon/examples/chess/grid.cm
+++ b/prosperon/examples/chess/grid.cm
@@ -1,57 +1,69 @@
-var CELLS = Symbol()
-
-var key = function key(x,y) { return `${x},${y}` }
-
-function grid(w, h)
-{
-  this[CELLS] = new Map()
-  this.width = w;
+function grid(w, h) {
+  this.width  = w;
   this.height = h;
+  // create a height×width array of empty lists
+  this.cells = new Array(h);
+  for (let y = 0; y < h; y++) {
+    this.cells[y] = new Array(w);
+    for (let x = 0; x < w; x++) {
+      this.cells[y][x] = [];     // each cell holds its own list
+    }
+  }
 }
 
 grid.prototype = {
-  cell(x,y) {
-    var k = key(x,y)
-    if (!this[CELLS].has(k)) this[CELLS].set(k,[])
-    return this[CELLS].get(k)
+  // return the array at (x,y)
+  cell(x, y) {
+    return this.cells[y][x];
   },
-  
+
+  // alias for cell
+  at(pos) {
+    return this.cell(pos.x, pos.y);
+  },
+
+  // add an entity into a cell
   add(entity, pos) {
     this.cell(pos.x, pos.y).push(entity);
     entity.coord = pos.slice();
   },
-  
-  remove(entity, pos) {
-    var c = this.cell(pos.x, pos.y);
-    c.splice(c.indexOf(entity), 1);
-  },
-  
-  at(pos) {
-    return this.cell(pos.x, pos.y);
-  },
-  
-  inBounds(pos) {
-    return pos.x >= 0 && pos.x < this.width && pos.y >= 0 && pos.y < this.height;
-  },
-  
-  each(fn) {
-    for (var [k, list] of this[CELLS])
-      for (var p of list) fn(p, p.coord);
-  },
-  
-  toString() {
-    var out = `grid [${this.width}x${this.height}]
-`
-    for (var y = 0; y < this.height; y++) {
-      for (var x = 0; x < this.width; x++) {
-        var cell = this.at([x,y]);
-        out += cell.length
-      }
-      if (y != this.height - 1) out += "\n"
-    }
-      
-    return out
-  },
-}
 
-return grid
+  // remove an entity from a cell
+  remove(entity, pos) {
+    const c = this.cell(pos.x, pos.y);
+    const i = c.indexOf(entity);
+    if (i !== -1) c.splice(i, 1);
+  },
+
+  // bounds check
+  inBounds(pos) {
+    return (
+      pos.x >= 0 && pos.x < this.width &&
+      pos.y >= 0 && pos.y < this.height
+    );
+  },
+
+  // call fn(entity, coord) for every entity in every cell
+  each(fn) {
+    for (let y = 0; y < this.height; y++) {
+      for (let x = 0; x < this.width; x++) {
+        const list = this.cells[y][x];
+        for (let entity of list) {
+          fn(entity, entity.coord);
+        }
+      }
+    }
+  },
+
+  // printable representation
+  toString() {
+    let out = `grid [${this.width}×${this.height}]\n`;
+    for (let y = 0; y < this.height; y++) {
+      for (let x = 0; x < this.width; x++) {
+        out += this.cells[y][x].length;
+      }
+      if (y !== this.height - 1) out += "\n";
+    }
+    return out;
+  }
+};
diff --git a/prosperon/graphics.cm b/prosperon/graphics.cm
index 48d7454c..331268f6 100644
--- a/prosperon/graphics.cm
+++ b/prosperon/graphics.cm
@@ -18,7 +18,7 @@ var CPU = Symbol()
 var LASTUSE = Symbol()
 var LOADING = Symbol()
 
-var cache = new Map()
+var cache = {}
 
 // Image constructor function
 graphics.Image = function(surfaceData) {
@@ -250,14 +250,14 @@ graphics.texture = function texture(path) {
     throw new Error('need a string for graphics.texture')
 
   var id = path //.split(':')[0]
-  if (cache.has(id)) return cache.get(id)
+  if (cache[id]) return cache[id]
   
   var ipath = res.find_image(id)
   if (!ipath)
     throw new Error(`unknown image ${id}`)
   
   var image = create_image(ipath)
-  cache.set(id, image)
+  cache[id] = image
   return image
 }
 graphics.texture[cell.DOC] = `
diff --git a/prosperon/resources.cm b/prosperon/resources.cm
index d170f973..80eaa962 100644
--- a/prosperon/resources.cm
+++ b/prosperon/resources.cm
@@ -2,12 +2,12 @@ var io = use('io')
 
 Object.defineProperty(Function.prototype, "hashify", {
   value: function () {
-    var hash = new Map()
+    var hash = {}
     var fn = this
     function hashified(...args) {
       var key = args[0]
-      if (!hash.has(key)) hash.set(key, fn(...args))
-      return hash.get(key)
+      if (hash[key] == null) hash[key] = fn(...args)
+      return hash[key]
     }
     return hashified
   },
diff --git a/scripts/engine.cm b/scripts/engine.cm
index 68999d8c..46f3dfaa 100644
--- a/scripts/engine.cm
+++ b/scripts/engine.cm
@@ -425,7 +425,7 @@ $_.connection[cell.DOC] = "The connection function takes a callback function, an
 
 var peers = {}
 var id_address = {}
-var peer_queue = new Map()
+var peer_queue = {}
 var portal = null
 var portal_fn = null