add memoize function and use it for makeEnvironment

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;

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;
+}

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
   };
-}
+});