diff --git a/web/static/src/ts/core/Widget.ts b/web/static/src/ts/core/base_widget.ts
similarity index 91%
rename from web/static/src/ts/core/Widget.ts
rename to web/static/src/ts/core/base_widget.ts
index acc7f7b3..aa435110 100644
--- a/web/static/src/ts/core/Widget.ts
+++ b/web/static/src/ts/core/base_widget.ts
@@ -23,8 +23,8 @@ interface Meta<T extends WEnv> {
   isStarted: boolean;
   isMounted: boolean;
   isDestroyed: boolean;
-  parent: Widget<T, {}> | null;
-  children: { [key: number]: Widget<T, {}> };
+  parent: BaseWidget<T, any, any> | null;
+  children: { [key: number]: BaseWidget<T, any, any> };
   // children mapping: from templateID to widgetID
   // should it be a map number => Widget?
   cmap: { [key: number]: number };
@@ -40,7 +40,7 @@ export interface Type<T> extends Function {
 // Widget
 //------------------------------------------------------------------------------
 
-export class Widget<T extends WEnv, Props> extends EventBus {
+export class BaseWidget<T extends WEnv, Props, State> extends EventBus {
   __widget__: Meta<WEnv>;
   template: string = "default";
   inlineTemplate: string | null = null;
@@ -52,13 +52,15 @@ export class Widget<T extends WEnv, Props> extends EventBus {
   env: T;
   state: Object = {};
   props: Props;
-  refs: { [key: string]: Widget<T, {}> | HTMLElement | undefined } = {};
+  refs: {
+    [key: string]: BaseWidget<T, any, any> | HTMLElement | undefined;
+  } = {};
 
   //--------------------------------------------------------------------------
   // Lifecycle
   //--------------------------------------------------------------------------
 
-  constructor(parent: Widget<T, any> | T, props?: Props) {
+  constructor(parent: BaseWidget<T, any, any> | T, props?: Props) {
     super();
     wl.push(this);
 
@@ -68,8 +70,8 @@ export class Widget<T extends WEnv, Props> extends EventBus {
     //   Pro: but creating widget (by a template) is always unsafe anyway
     this.props = <Props>props;
     let id: number;
-    let p: Widget<T, any> | null = null;
-    if (parent instanceof Widget) {
+    let p: BaseWidget<T, any, any> | null = null;
+    if (parent instanceof BaseWidget) {
       p = parent;
       this.env = parent.env;
       id = this.env.getID();
@@ -173,17 +175,11 @@ export class Widget<T extends WEnv, Props> extends EventBus {
    * - it is ok to call updateState before the widget is started. In that
    * case, it will simply update the state and will not rerender
    */
-  async updateState(nextState: Object) {
+  async updateState(nextState: Partial<State>) {
     if (Object.keys(nextState).length === 0) {
       return;
     }
-    for (let key in nextState) {
-      if (key in this.state) {
-        this.state[key] = nextState[key];
-      } else {
-        throw new Error(`Invalid key: '${key}' does not exist in widget state`);
-      }
-    }
+    Object.assign(this.state, nextState);
     if (this.__widget__.isStarted) {
       return this.render();
     }
@@ -259,7 +255,7 @@ export class Widget<T extends WEnv, Props> extends EventBus {
     }
   }
 
-  private visitSubTree(callback: (w: Widget<T, any>) => boolean) {
+  private visitSubTree(callback: (w: BaseWidget<T, any, any>) => boolean) {
     const shouldVisitChildren = callback(this);
     if (shouldVisitChildren) {
       const children = this.__widget__.children;
diff --git a/web/static/src/ts/env.ts b/web/static/src/ts/env.ts
index 241101c2..3705efb8 100644
--- a/web/static/src/ts/env.ts
+++ b/web/static/src/ts/env.ts
@@ -1,18 +1,22 @@
-import { QWeb } from "./core/qweb_vdom";
-import { idGenerator, memoize } from "./core/utils";
-import { WEnv } from "./core/widget";
-import { ActionManager, IActionManager } from "./services/action_manager";
 import { Ajax, IAjax } from "./core/ajax";
+import { WEnv } from "./core/base_widget";
 import {
   INotificationManager,
   NotificationManager
 } from "./core/notifications";
-import { actionRegistry } from "./registries";
+import { QWeb } from "./core/qweb_vdom";
 import { Registry } from "./core/registry";
 import { IRouter, Router } from "./core/router";
+import { idGenerator, memoize } from "./core/utils";
+import { actionRegistry } from "./registries";
+import {
+  ActionManager,
+  ActionWidget,
+  IActionManager
+} from "./services/action_manager";
 import { CRM } from "./widgets/crm";
 import { Discuss } from "./widgets/discuss";
-import { Widget, Type } from "./core/widget";
+
 //------------------------------------------------------------------------------
 // Types
 //------------------------------------------------------------------------------
@@ -30,7 +34,7 @@ export interface Env extends WEnv {
   router: IRouter;
 
   // registries
-  actionRegistry: Registry<Type<Widget<Env, any>>>;
+  actionRegistry: Registry<ActionWidget>;
 
   // data
   menus: Menu[];
diff --git a/web/static/src/ts/registries.ts b/web/static/src/ts/registries.ts
index bf97d29e..7aa514fb 100644
--- a/web/static/src/ts/registries.ts
+++ b/web/static/src/ts/registries.ts
@@ -1,5 +1,4 @@
 import { Registry } from "./core/registry";
-import { Widget, Type } from "./core/widget";
-import { Env } from "./env";
+import { ActionWidget } from "./services/action_manager";
 
-export const actionRegistry: Registry<Type<Widget<Env, any>>> = new Registry();
+export const actionRegistry: Registry<ActionWidget> = new Registry();
diff --git a/web/static/src/ts/services/action_manager.ts b/web/static/src/ts/services/action_manager.ts
index 5ec80570..65ccdb1a 100644
--- a/web/static/src/ts/services/action_manager.ts
+++ b/web/static/src/ts/services/action_manager.ts
@@ -1,7 +1,7 @@
+import { Type } from "../core/base_widget";
 import { EventBus } from "../core/event_bus";
 import { Registry } from "../core/registry";
-import { Type, Widget } from "../core/widget";
-import { Env } from "../env";
+import { Widget } from "../widgets/widget";
 
 //------------------------------------------------------------------------------
 // Types
@@ -18,10 +18,12 @@ export interface CommonActionInfo {
   target: "current" | "new";
 }
 
+export type ActionWidget = Type<Widget<{}, {}>>;
+
 export interface ClientActionInfo extends CommonActionInfo {
   type: "client";
   name: string;
-  Widget: Type<Widget<Env, {}>>;
+  Widget: ActionWidget;
 }
 
 export interface ActWindowInfo extends CommonActionInfo {
@@ -47,10 +49,10 @@ export interface IActionManager {
 //------------------------------------------------------------------------------
 
 export class ActionManager extends EventBus implements IActionManager {
-  registry: Registry<Type<Widget<Env, any>>>;
+  registry: Registry<ActionWidget>;
   stack: ActionStack;
 
-  constructor(registry: Registry<Type<Widget<Env, any>>>) {
+  constructor(registry: Registry<ActionWidget>) {
     super();
     this.registry = registry;
     this.stack = [];
diff --git a/web/static/src/ts/widgets/CRM.ts b/web/static/src/ts/widgets/CRM.ts
index b4f88564..b8912398 100644
--- a/web/static/src/ts/widgets/CRM.ts
+++ b/web/static/src/ts/widgets/CRM.ts
@@ -1,6 +1,5 @@
-import { Widget } from "../core/widget";
-import { Env } from "../env";
+import { Widget } from "./widget";
 
-export class CRM extends Widget<Env, {}> {
+export class CRM extends Widget<{}, {}> {
   template = "web.crm";
 }
diff --git a/web/static/src/ts/widgets/Counter.ts b/web/static/src/ts/widgets/Counter.ts
index f42a8b94..43fce3e7 100644
--- a/web/static/src/ts/widgets/Counter.ts
+++ b/web/static/src/ts/widgets/Counter.ts
@@ -1,22 +1,34 @@
-import { Widget } from "../core/widget";
-import { Env } from "../env";
+import { Widget } from "./widget";
+
+//------------------------------------------------------------------------------
+// Types
+//------------------------------------------------------------------------------
 
 interface Props {
   initialState?: number;
 }
 
-export class Counter extends Widget<Env, Props> {
+interface State {
+  counter: number;
+}
+
+//------------------------------------------------------------------------------
+// Counter
+//------------------------------------------------------------------------------
+
+export class Counter extends Widget<Props, State> {
   inlineTemplate = `
     <div t-name="counter">
       <button t-on-click="increment(-1)">-</button>
       <span style="font-weight:bold">Value: <t t-esc="state.counter"/></span>
       <button t-on-click="increment(1)">+</button>
     </div>`;
+
   state = {
     counter: 0
   };
 
-  constructor(parent: Widget<Env, {}>, props: Props) {
+  constructor(parent: Widget<any, any>, props: Props) {
     super(parent, props);
     this.state.counter = props.initialState || 0;
   }
diff --git a/web/static/src/ts/widgets/Discuss.ts b/web/static/src/ts/widgets/Discuss.ts
index 896b9985..5cced964 100644
--- a/web/static/src/ts/widgets/Discuss.ts
+++ b/web/static/src/ts/widgets/Discuss.ts
@@ -1,9 +1,21 @@
-import { Widget } from "../core/widget";
-import { Env } from "../env";
 import { Clock } from "./clock";
 import { Counter } from "./counter";
+import { Widget } from "./widget";
 
-export class Discuss extends Widget<Env, {}> {
+//------------------------------------------------------------------------------
+// Types
+//------------------------------------------------------------------------------
+
+interface State {
+  validcounter: boolean;
+  color: "red" | "blue";
+}
+
+//------------------------------------------------------------------------------
+// Discuss
+//------------------------------------------------------------------------------
+
+export class Discuss extends Widget<{}, State> {
   template = "web.discuss";
   widgets = { Clock, Counter, ColorWidget };
   state = { validcounter: true, color: "red" };
@@ -38,7 +50,7 @@ export class Discuss extends Widget<Env, {}> {
   }
 }
 
-class ColorWidget extends Widget<Env, { color: "red" | "blue" }> {
+class ColorWidget extends Widget<{ color: "red" | "blue" }, {}> {
   inlineTemplate = `
     <div t-name="colorwidget">
       <span>Current Color: </span>
diff --git a/web/static/src/ts/widgets/Navbar.ts b/web/static/src/ts/widgets/Navbar.ts
index f8fb8c21..4145c0b2 100644
--- a/web/static/src/ts/widgets/Navbar.ts
+++ b/web/static/src/ts/widgets/Navbar.ts
@@ -1,13 +1,21 @@
-import { Widget } from "../core/widget";
-import { Env, Menu } from "../env";
+import { Menu } from "../env";
 import { MenuItem } from "../misc/menu_helpers";
+import { Widget } from "./widget";
+
+//------------------------------------------------------------------------------
+// Types
+//------------------------------------------------------------------------------
 
 export interface Props {
   inHome: boolean;
   app: MenuItem | null;
 }
 
-export class Navbar extends Widget<Env, Props> {
+//------------------------------------------------------------------------------
+// Navbar
+//------------------------------------------------------------------------------
+
+export class Navbar extends Widget<Props, {}> {
   template = "web.navbar";
 
   getUrl(menu: Menu) {
diff --git a/web/static/src/ts/widgets/action_container.ts b/web/static/src/ts/widgets/action_container.ts
index 08b4cb2d..a898e9de 100644
--- a/web/static/src/ts/widgets/action_container.ts
+++ b/web/static/src/ts/widgets/action_container.ts
@@ -1,12 +1,19 @@
-import { Widget } from "../core/widget";
-import { Env } from "../env";
 import { ActionStack } from "../services/action_manager";
+import { Widget } from "./widget";
+
+//------------------------------------------------------------------------------
+// Types
+//------------------------------------------------------------------------------
 
 export interface Props {
   stack: ActionStack;
 }
 
-export class ActionContainer extends Widget<Env, Props> {
+//------------------------------------------------------------------------------
+// Action Container
+//------------------------------------------------------------------------------
+
+export class ActionContainer extends Widget<Props, {}> {
   template = "web.action_container";
   currentWidget: any;
 
diff --git a/web/static/src/ts/widgets/clock.ts b/web/static/src/ts/widgets/clock.ts
index 01552374..f08b2305 100644
--- a/web/static/src/ts/widgets/clock.ts
+++ b/web/static/src/ts/widgets/clock.ts
@@ -1,7 +1,18 @@
-import { Widget } from "../core/widget";
-import { Env } from "../env";
+import { Widget } from "./widget";
 
-export class Clock extends Widget<Env, {}> {
+//------------------------------------------------------------------------------
+// Types
+//------------------------------------------------------------------------------
+
+interface State {
+  currentTime: string;
+}
+
+//------------------------------------------------------------------------------
+// Clock
+//------------------------------------------------------------------------------
+
+export class Clock extends Widget<{}, State> {
   inlineTemplate = `<div class="o_clock"><t t-esc="state.currentTime"/></div>`;
   timeout: any | undefined;
 
diff --git a/web/static/src/ts/widgets/home_menu.ts b/web/static/src/ts/widgets/home_menu.ts
index aba94737..2fc02511 100644
--- a/web/static/src/ts/widgets/home_menu.ts
+++ b/web/static/src/ts/widgets/home_menu.ts
@@ -1,6 +1,5 @@
-import { Widget } from "../core/widget";
-import { Env } from "../env";
 import { MenuInfo, MenuItem } from "../misc/menu_helpers";
+import { Widget } from "./widget";
 
 //------------------------------------------------------------------------------
 // Types
@@ -14,7 +13,7 @@ export interface Props {
 // Home Menu
 //------------------------------------------------------------------------------
 
-export class HomeMenu extends Widget<Env, Props> {
+export class HomeMenu extends Widget<Props, {}> {
   template = "web.home_menu";
 
   get apps(): MenuItem[] {
diff --git a/web/static/src/ts/widgets/notification.ts b/web/static/src/ts/widgets/notification.ts
index a6432e83..c4a7a7c5 100644
--- a/web/static/src/ts/widgets/notification.ts
+++ b/web/static/src/ts/widgets/notification.ts
@@ -1,8 +1,7 @@
-import { Widget } from "../core/widget";
-import { Env } from "../env";
 import { INotification } from "../core/notifications";
+import { Widget } from "./widget";
 
-export class Notification extends Widget<Env, INotification> {
+export class Notification extends Widget<INotification, {}> {
   template = "web.notification";
 
   close() {
diff --git a/web/static/src/ts/widgets/root.ts b/web/static/src/ts/widgets/root.ts
index 02cc30ea..b3adbf53 100644
--- a/web/static/src/ts/widgets/root.ts
+++ b/web/static/src/ts/widgets/root.ts
@@ -1,5 +1,5 @@
 import { INotification } from "../core/notifications";
-import { Widget } from "../core/widget";
+import { Widget } from "./widget";
 import { Env } from "../env";
 import { MenuInfo, MenuItem, getAppAndAction } from "../misc/menu_helpers";
 import { ActionStack } from "../services/action_manager";
@@ -28,7 +28,7 @@ interface Props {
 // Root Widget
 //------------------------------------------------------------------------------
 
-export class Root extends Widget<Env, Props> {
+export class Root extends Widget<Props, State> {
   template = "web.web_client";
   widgets = { Navbar, Notification, HomeMenu, ActionContainer };
 
diff --git a/web/static/src/ts/widgets/widget.ts b/web/static/src/ts/widgets/widget.ts
new file mode 100644
index 00000000..6ec33baf
--- /dev/null
+++ b/web/static/src/ts/widgets/widget.ts
@@ -0,0 +1,4 @@
+import { BaseWidget } from "../core/base_widget";
+import { Env } from "../env";
+
+export class Widget<Props, State> extends BaseWidget<Env, Props, State> {}
diff --git a/web/static/tests/core/widget.test.ts b/web/static/tests/core/base_widget.test.ts
similarity index 90%
rename from web/static/tests/core/widget.test.ts
rename to web/static/tests/core/base_widget.test.ts
index 4372705d..2b073856 100644
--- a/web/static/tests/core/widget.test.ts
+++ b/web/static/tests/core/base_widget.test.ts
@@ -1,6 +1,5 @@
-import { WEnv, Widget } from "../../src/ts/core/widget";
-import { makeTestWEnv, makeTestFixture } from "../helpers";
-import { normalize } from "../helpers";
+import { BaseWidget, WEnv } from "../../src/ts/core/base_widget";
+import { makeTestFixture, makeTestWEnv, normalize } from "../helpers";
 
 //------------------------------------------------------------------------------
 // Setup and helpers
@@ -34,13 +33,16 @@ function nextTick(): Promise<void> {
   return Promise.resolve();
 }
 
-function children(w: Widget<WEnv, {}>): Widget<WEnv, {}>[] {
+class Widget extends BaseWidget<WEnv, {}, {}> {}
+
+function children(w: Widget): Widget[] {
   const childrenMap = w.__widget__.children;
   return Object.keys(childrenMap).map(id => childrenMap[id]);
 }
 
 // Test widgets
-class Counter extends Widget<WEnv, {}> {
+class Counter extends Widget {
+  // class Counter extends Widget<WEnv, {}, {counter: number}> {
   template = "counter";
   state = {
     counter: 0
@@ -51,12 +53,12 @@ class Counter extends Widget<WEnv, {}> {
   }
 }
 
-class WidgetA extends Widget<WEnv, {}> {
+class WidgetA extends Widget {
   template = "widgetA";
   widgets = { b: WidgetB };
 }
 
-class WidgetB extends Widget<WEnv, {}> {
+class WidgetB extends Widget {
   template = "widgetB";
 }
 
@@ -88,7 +90,7 @@ describe("basic widget properties", () => {
   });
 
   test("widget style and classname", async () => {
-    class StyledWidget extends Widget<WEnv, {}> {
+    class StyledWidget extends Widget {
       inlineTemplate = `<div style="font-weight:bold;" class="some-class">world</div>`;
     }
     const widget = new StyledWidget(env);
@@ -100,7 +102,7 @@ describe("basic widget properties", () => {
 
   test("updateState before first render does not trigger a render", async () => {
     let renderCalls = 0;
-    class TestW extends Widget<WEnv, {}> {
+    class TestW extends Widget {
       async willStart() {
         this.updateState({});
       }
@@ -142,7 +144,7 @@ describe("basic widget properties", () => {
 describe("lifecycle hooks", () => {
   test("willStart hook is called", async () => {
     let willstart = false;
-    class HookWidget extends Widget<WEnv, {}> {
+    class HookWidget extends Widget {
       async willStart() {
         willstart = true;
       }
@@ -154,7 +156,7 @@ describe("lifecycle hooks", () => {
 
   test("mounted hook is not called if not in DOM", async () => {
     let mounted = false;
-    class HookWidget extends Widget<WEnv, {}> {
+    class HookWidget extends Widget {
       async mounted() {
         mounted = true;
       }
@@ -167,7 +169,7 @@ describe("lifecycle hooks", () => {
 
   test("mounted hook is called if mounted in DOM", async () => {
     let mounted = false;
-    class HookWidget extends Widget<WEnv, {}> {
+    class HookWidget extends Widget {
       async mounted() {
         mounted = true;
       }
@@ -179,11 +181,11 @@ describe("lifecycle hooks", () => {
 
   test("willStart hook is called on subwidget", async () => {
     let ok = false;
-    class ParentWidget extends Widget<WEnv, {}> {
+    class ParentWidget extends Widget {
       inlineTemplate = `<div><t t-widget="child"/></div>`;
       widgets = { child: ChildWidget };
     }
-    class ChildWidget extends Widget<WEnv, {}> {
+    class ChildWidget extends Widget {
       async willStart() {
         ok = true;
       }
@@ -197,7 +199,7 @@ describe("lifecycle hooks", () => {
     expect.assertions(4);
     let parentMounted = false;
     let childMounted = false;
-    class ParentWidget extends Widget<WEnv, {}> {
+    class ParentWidget extends Widget {
       inlineTemplate = `<div><t t-widget="child"/></div>`;
       widgets = { child: ChildWidget };
       mounted() {
@@ -205,7 +207,7 @@ describe("lifecycle hooks", () => {
         parentMounted = true;
       }
     }
-    class ChildWidget extends Widget<WEnv, {}> {
+    class ChildWidget extends Widget {
       mounted() {
         expect(document.body.contains(this.el)).toBe(true);
         expect(parentMounted).toBe(true);
@@ -223,7 +225,7 @@ describe("lifecycle hooks", () => {
     // the t-else part in the template is important. This is
     // necessary to have a situation that could confuse the vdom
     // patching algorithm
-    class ParentWidget extends Widget<WEnv, {}> {
+    class ParentWidget extends Widget {
       inlineTemplate = `
           <div>
             <t t-if="state.ok">
@@ -236,7 +238,7 @@ describe("lifecycle hooks", () => {
       state = { ok: false };
       widgets = { child: ChildWidget };
     }
-    class ChildWidget extends Widget<WEnv, {}> {
+    class ChildWidget extends Widget {
       async willStart() {
         hookCounter++;
       }
@@ -261,13 +263,13 @@ describe("lifecycle hooks", () => {
     expect.assertions(1);
     const target = document.createElement("div");
     document.body.appendChild(target);
-    class ParentWidget extends Widget<WEnv, {}> {
+    class ParentWidget extends Widget {
       mounted() {
         const child = new ChildWidget(this);
         child.mount(this.el!);
       }
     }
-    class ChildWidget extends Widget<WEnv, {}> {
+    class ChildWidget extends Widget {
       mounted() {
         expect(this.el).toBeTruthy();
         done();
@@ -279,7 +281,7 @@ describe("lifecycle hooks", () => {
 
   test("widgets are unmounted and destroyed if no longer in DOM", async () => {
     let steps: string[] = [];
-    class ParentWidget extends Widget<WEnv, {}> {
+    class ParentWidget extends Widget {
       state = { ok: true };
       inlineTemplate = `<div>
         <t t-if="state.ok"><t t-widget="child"/></t>
@@ -287,7 +289,7 @@ describe("lifecycle hooks", () => {
       widgets = { child: ChildWidget };
     }
 
-    class ChildWidget extends Widget<WEnv, {}> {
+    class ChildWidget extends Widget {
       constructor(parent) {
         super(parent);
         steps.push("init");
@@ -320,7 +322,7 @@ describe("lifecycle hooks", () => {
 
   test("hooks are called in proper order in widget creation/destruction", async () => {
     let steps: string[] = [];
-    class ParentWidget extends Widget<WEnv, {}> {
+    class ParentWidget extends Widget {
       inlineTemplate = `<div><t t-widget="child"/></div>`;
       widgets = { child: ChildWidget };
       constructor(parent) {
@@ -341,7 +343,7 @@ describe("lifecycle hooks", () => {
       }
     }
 
-    class ChildWidget extends Widget<WEnv, {}> {
+    class ChildWidget extends Widget {
       constructor(parent) {
         super(parent);
         steps.push("c init");
@@ -378,7 +380,7 @@ describe("lifecycle hooks", () => {
 
   test("shouldUpdate hook prevent rerendering", async () => {
     let shouldUpdate = false;
-    class TestWidget extends Widget<WEnv, {}> {
+    class TestWidget extends Widget {
       inlineTemplate = `<div><t t-esc="props.val"/></div>`;
       shouldUpdate() {
         return shouldUpdate;
@@ -408,7 +410,7 @@ describe("destroy method", () => {
 
   test("destroying a widget twice only call destroyed once", async () => {
     let count = 0;
-    class TestWidget extends Widget<WEnv, {}> {
+    class TestWidget extends Widget {
       destroyed() {
         count++;
       }
@@ -450,7 +452,7 @@ describe("destroy method", () => {
     let p: Promise<void> = new Promise(function(r) {
       resolve = r;
     });
-    class DelayedWidget extends Widget<WEnv, {}> {
+    class DelayedWidget extends Widget {
       willStart() {
         return p;
       }
@@ -490,7 +492,7 @@ describe("composition", () => {
   });
 
   test("t-refs on widget are widgets", async () => {
-    class WidgetC extends Widget<WEnv, {}> {
+    class WidgetC extends Widget {
       inlineTemplate = `<div>Hello<t t-ref="mywidgetb" t-widget="b"/></div>`;
       widgets = { b: WidgetB };
     }
@@ -500,7 +502,7 @@ describe("composition", () => {
   });
 
   test("modifying a sub widget", async () => {
-    class ParentWidget extends Widget<WEnv, {}> {
+    class ParentWidget extends Widget {
       inlineTemplate = `<div><t t-widget="Counter"/></div>`;
       widgets = { Counter };
     }
@@ -538,7 +540,7 @@ describe("composition", () => {
   });
 
   test("rerendering a widget with a sub widget", async () => {
-    class ParentWidget extends Widget<WEnv, {}> {
+    class ParentWidget extends Widget {
       inlineTemplate = `<div><t t-widget="Counter"/></div>`;
       widgets = { Counter };
     }
@@ -557,7 +559,7 @@ describe("composition", () => {
   });
 
   test("sub widgets are destroyed if no longer in dom, then recreated", async () => {
-    class ParentWidget extends Widget<WEnv, {}> {
+    class ParentWidget extends Widget {
       state = { ok: true };
       inlineTemplate = `<div><t t-if="state.ok"><t t-widget="counter"/></t></div>`;
       widgets = { counter: Counter };
@@ -579,7 +581,7 @@ describe("composition", () => {
   });
 
   test("sub widgets with t-keep-alive are not destroyed if no longer in dom", async () => {
-    class ParentWidget extends Widget<WEnv, {}> {
+    class ParentWidget extends Widget {
       state = { ok: true };
       inlineTemplate = `<div><t t-if="state.ok"><t t-widget="counter" t-keep-alive="1"/></t></div>`;
       widgets = { counter: Counter };
@@ -605,12 +607,12 @@ describe("composition", () => {
   });
 
   test("sub widgets dom state with t-keep-alive is preserved", async () => {
-    class ParentWidget extends Widget<WEnv, {}> {
+    class ParentWidget extends Widget {
       state = { ok: true };
       inlineTemplate = `<div><t t-if="state.ok"><t t-widget="InputWidget" t-keep-alive="1"/></t></div>`;
       widgets = { InputWidget };
     }
-    class InputWidget extends Widget<WEnv, {}> {
+    class InputWidget extends Widget {
       inlineTemplate = "<input/>";
     }
     const widget = new ParentWidget(env);
@@ -627,11 +629,11 @@ describe("composition", () => {
   });
 
   test("sub widgets rendered in a loop", async () => {
-    class ChildWidget extends Widget<WEnv, { n: number }> {
+    class ChildWidget extends Widget {
       inlineTemplate = `<span><t t-esc="props.n"/></span>`;
     }
 
-    class Parent extends Widget<WEnv, {}> {
+    class Parent extends Widget {
       inlineTemplate = `
         <div>
           <t t-foreach="state.numbers" t-as="number">
@@ -658,7 +660,7 @@ describe("composition", () => {
 
   test("sub widgets with some state rendered in a loop", async () => {
     let n = 1;
-    class ChildWidget extends Widget<WEnv, never> {
+    class ChildWidget extends Widget {
       inlineTemplate = `<span><t t-esc="state.n"/></span>`;
       constructor(parent) {
         super(parent);
@@ -667,7 +669,7 @@ describe("composition", () => {
       }
     }
 
-    class Parent extends Widget<WEnv, {}> {
+    class Parent extends Widget {
       inlineTemplate = `<div>
           <t t-foreach="state.numbers" t-as="number">
             <t t-widget="ChildWidget" t-key="number"/>
@@ -694,13 +696,13 @@ describe("composition", () => {
 
 describe("props evaluation (with t-props directive)", () => {
   test("explicit object prop", async () => {
-    class Parent extends Widget<WEnv, {}> {
+    class Parent extends Widget {
       inlineTemplate = `<div><t t-widget="child" t-props="{value: state.val}"/></div>`;
       widgets = { child: Child };
       state = { val: 42 };
     }
 
-    class Child extends Widget<WEnv, {}> {
+    class Child extends Widget {
       inlineTemplate = `<span><t t-esc="state.someval"/></span>`;
       state: { someval: number };
       constructor(parent: Parent, props: { value: number }) {
@@ -715,13 +717,13 @@ describe("props evaluation (with t-props directive)", () => {
   });
 
   test("object prop value", async () => {
-    class Parent extends Widget<WEnv, {}> {
+    class Parent extends Widget {
       inlineTemplate = `<div><t t-widget="child" t-props="state"/></div>`;
       widgets = { child: Child };
       state = { val: 42 };
     }
 
-    class Child extends Widget<WEnv, {}> {
+    class Child extends Widget {
       inlineTemplate = `<span><t t-esc="state.someval"/></span>`;
       state: { someval: number };
       constructor(parent: Parent, props: { val: number }) {
@@ -739,7 +741,7 @@ describe("props evaluation (with t-props directive)", () => {
 describe("t-on directive on widgets", () => {
   test("t-on works as expected", async () => {
     let n = 0;
-    class ParentWidget extends Widget<WEnv, {}> {
+    class ParentWidget extends Widget {
       inlineTemplate = `<div><t t-widget="child" t-on-customevent="someMethod"/></div>`;
       widgets = { child: Child };
       someMethod(arg) {
@@ -747,7 +749,7 @@ describe("t-on directive on widgets", () => {
         n++;
       }
     }
-    class Child extends Widget<WEnv, {}> {}
+    class Child extends Widget {}
     const widget = new ParentWidget(env);
     await widget.mount(fixture);
     let child = children(widget)[0];
@@ -765,7 +767,7 @@ describe("random stuff/miscellaneous", () => {
     // this test makes sure that the foreach directive does not pollute sub
     // context with the inLoop variable, which is then used in the t-widget
     // directive as a key
-    class Test extends Widget<WEnv, {}> {
+    class Test extends Widget {
       inlineTemplate = `<div><t t-foreach="2">txt</t><t t-widget="widget"/></div>`;
       widgets = { widget: Widget };
     }
@@ -778,13 +780,13 @@ describe("random stuff/miscellaneous", () => {
     // in this situation, we protect against a bug that occurred: because of the
     // interplay between widgets and vnodes, a sub widget vnode was patched
     // twice.
-    class Parent extends Widget<WEnv, {}> {
+    class Parent extends Widget {
       inlineTemplate = `<div><t t-widget="child" t-props="state"/></div>`;
       widgets = { child: Child };
       state = { flag: false };
     }
 
-    class Child extends Widget<WEnv, {}> {
+    class Child extends Widget {
       inlineTemplate = `<span>abc<t t-if="props.flag">def</t></span>`;
     }
 
diff --git a/web/static/tests/helpers.ts b/web/static/tests/helpers.ts
index 0d6fb86e..0d67a1d9 100644
--- a/web/static/tests/helpers.ts
+++ b/web/static/tests/helpers.ts
@@ -1,6 +1,6 @@
 import { QWeb } from "../src/ts/core/qweb_vdom";
 import { idGenerator } from "../src/ts/core/utils";
-import { WEnv } from "../src/ts/core/widget";
+import { WEnv } from "../src/ts/core/base_widget";
 import { Env } from "../src/ts/env";
 import { IAjax, RPCQuery } from "../src/ts/core/ajax";
 import { Registry } from "../src/ts/core/registry";