diff --git a/web/static/src/ts/core/Widget.ts b/web/static/src/ts/core/Widget.ts
index d65da5ca..7f4d4485 100644
--- a/web/static/src/ts/core/Widget.ts
+++ b/web/static/src/ts/core/Widget.ts
@@ -15,7 +15,7 @@ let wl: any[] = [];
 (<any>window).wl = wl;
 
 interface Meta<T extends WEnv> {
-  id: number;
+  readonly id: number;
   // name: string;
   // template: string;
   vnode: VNode | null;
diff --git a/web/static/src/ts/core/utils.ts b/web/static/src/ts/core/utils.ts
index 74cb005b..06ff89d8 100644
--- a/web/static/src/ts/core/utils.ts
+++ b/web/static/src/ts/core/utils.ts
@@ -31,3 +31,23 @@ export function idGenerator(): (() => number) {
   let nextID = 1;
   return () => nextID++;
 }
+
+export type HashFn = (args: any[]) => string;
+
+export function memoize<R, T extends (...args: any[]) => R>(
+  f: T,
+  hash?: HashFn
+): T {
+  if (!hash) {
+    hash = args => args.map(a => String(a)).join(",");
+  }
+  let cache: { [key: string]: R } = {};
+  function memoizedFunction(...args: any[]) {
+    let hashValue = hash!(args);
+    if (!(hashValue in cache)) {
+      cache[hashValue] = f(...args);
+    }
+    return cache[hashValue];
+  }
+  return memoizedFunction as T;
+}
diff --git a/web/static/src/ts/env.ts b/web/static/src/ts/env.ts
index 68082760..41eb94ce 100644
--- a/web/static/src/ts/env.ts
+++ b/web/static/src/ts/env.ts
@@ -1,5 +1,5 @@
 import { QWeb } from "./core/qweb_vdom";
-import { idGenerator } from "./core/utils";
+import { idGenerator, memoize } from "./core/utils";
 import { WEnv } from "./core/widget";
 import { ActionManager, IActionManager } from "./services/action_manager";
 import { Ajax, IAjax } from "./services/ajax";
@@ -32,7 +32,17 @@ export interface Env extends WEnv {
 // Code
 //------------------------------------------------------------------------------
 
-export function makeEnvironment(): Env {
+/**
+ * makeEnvironment returns the main environment for the application.
+ *
+ * Note that it does not make much sense (except for tests) to have more than
+ * one environment. For example, with two environment, the router code in one
+ * environment will probably interfere with the code from the other environment.
+ *
+ * For this reason, the result of makeEnvironment is memoized: every call to
+ * this function will actually return the same environment.
+ */
+export const makeEnvironment = memoize(function(): Env {
   const qweb = new QWeb();
   const router = new Router();
   const ajax = new Ajax();
@@ -55,4 +65,4 @@ export function makeEnvironment(): Env {
     rpc: ajax.rpc,
     debug: false
   };
-}
+});
diff --git a/web/static/tests/core/utils.test.ts b/web/static/tests/core/utils.test.ts
index e5374adb..443b4fa3 100644
--- a/web/static/tests/core/utils.test.ts
+++ b/web/static/tests/core/utils.test.ts
@@ -1,4 +1,9 @@
-import { escape, htmlTrim, idGenerator } from "../../src/ts/core/utils";
+import {
+  escape,
+  htmlTrim,
+  idGenerator,
+  memoize
+} from "../../src/ts/core/utils";
 
 describe("escape", () => {
   test("normal strings", () => {
@@ -34,3 +39,23 @@ describe("idGenerator", () => {
     expect(gen()).toBe(3);
   });
 });
+
+describe("memoize", () => {
+  test("return correct value", () => {
+    const f = memoize((a, b) => a + b);
+    expect(f(1, 3)).toBe(4);
+  });
+
+  test("does not recompute if not needed", () => {
+    let nCalls = 0;
+    function origFunction(a: number, b: number): number {
+      nCalls++;
+      return a + b;
+    }
+    const memoized = memoize(origFunction);
+
+    expect(memoized(1, 3)).toBe(4);
+    expect(memoized(1, 3)).toBe(4);
+    expect(nCalls).toBe(1);
+  });
+});