diff --git a/.npmignore b/.npmignore
index 17077e2..78f5ce2 100644
--- a/.npmignore
+++ b/.npmignore
@@ -1,9 +1,11 @@
 .eslintrc.json
 jest.config.ts
 test/
+preview/
 .parcel-cache/
 Contributing.md
 docs/
 .husky/
 .github/
-.vscode/
\ No newline at end of file
+.vscode/
+.vercel/
\ No newline at end of file
diff --git a/ReadMe.md b/ReadMe.md
index b620bc4..63b456f 100644
--- a/ReadMe.md
+++ b/ReadMe.md
@@ -45,7 +45,7 @@ Demo & **GitHub template**: https://web-cell.dev/scaffold/
 ```shell
 npm init -y
 npm install dom-renderer mobx web-cell
-npm install parcel -D
+npm install parcel @parcel/config-default "@parcel/transformer-typescript-tsc" -D
 ```
 
 #### `package.json`
@@ -73,6 +73,17 @@ npm install parcel -D
 }
 ```
 
+#### `.parcelrc`
+
+```json
+{
+    "extends": "@parcel/config-default",
+    "transformers": {
+        "*.{ts,tsx}": ["@parcel/transformer-typescript-tsc"]
+    }
+}
+```
+
 #### `source/index.html`
 
 ```html
diff --git a/preview/Clock.tsx b/preview/Clock.tsx
new file mode 100644
index 0000000..904e1d3
--- /dev/null
+++ b/preview/Clock.tsx
@@ -0,0 +1,40 @@
+import { observable } from 'mobx';
+import { Second } from 'web-utility';
+import { component, observer } from '../source';
+
+class ClockModel {
+    @observable
+    accessor time = new Date();
+
+    constructor() {
+        setInterval(() => (this.time = new Date()), Second);
+    }
+}
+
+const clockStore = new ClockModel();
+
+export const FunctionClock = observer(() => {
+    const { time } = clockStore;
+
+    return (
+        <time dateTime={time.toJSON()}>
+            Function Clock: {time.toLocaleString()}
+        </time>
+    );
+});
+
+@component({ tagName: 'class-clock' })
+@observer
+export class ClassClock extends HTMLElement {
+    state = new ClockModel();
+
+    render() {
+        const { time } = this.state;
+
+        return (
+            <time dateTime={time.toJSON()}>
+                Class Clock: {time.toLocaleString()}
+            </time>
+        );
+    }
+}
diff --git a/preview/Home.tsx b/preview/Home.tsx
index 9aa276f..08b9614 100644
--- a/preview/Home.tsx
+++ b/preview/Home.tsx
@@ -1,38 +1,27 @@
-import { configure, observable } from 'mobx';
-import { component, observer } from '../source';
+import { ClassClock, FunctionClock } from './Clock';
 
-configure({ enforceActions: 'never' });
-
-@component({ tagName: 'home-page' })
-@observer
-export class HomePage extends HTMLElement {
-    @observable
-    accessor time = '';
-
-    connectedCallback() {
-        setInterval(() => (this.time = new Date().toLocaleString()), 1000);
-    }
-
-    render() {
-        const { time } = this;
-
-        return (
-            <>
-                <h1>Hello Vanilla!</h1>
-                <div>
-                    We use the same configuration as Parcel to bundle this
-                    sandbox, you can find more info about Parcel
-                    <a
-                        href="https://parceljs.org"
-                        target="_blank"
-                        rel="noopener noreferrer"
-                    >
-                        here
-                    </a>
-                    .
-                </div>
-                <time>{time}</time>
-            </>
-        );
-    }
-}
+export const HomePage = () => (
+    <>
+        <h1>Hello Vanilla!</h1>
+        <div>
+            We use the same configuration as Parcel to bundle this sandbox, you
+            can find more info about Parcel
+            <a
+                href="https://parceljs.org"
+                target="_blank"
+                rel="noopener noreferrer"
+            >
+                here
+            </a>
+            .
+        </div>
+        <ul>
+            <li>
+                <FunctionClock />
+            </li>
+            <li>
+                <ClassClock />
+            </li>
+        </ul>
+    </>
+);
diff --git a/preview/index.tsx b/preview/index.tsx
index 8a2b5a5..ce22449 100644
--- a/preview/index.tsx
+++ b/preview/index.tsx
@@ -1,5 +1,8 @@
 import { DOMRenderer } from 'dom-renderer';
+import { configure } from 'mobx';
 
 import { HomePage } from './Home';
 
+configure({ enforceActions: 'never' });
+
 new DOMRenderer().render(<HomePage />, document.querySelector('#app')!);
diff --git a/source/index.ts b/source/index.ts
index 4c646b4..7620e5d 100644
--- a/source/index.ts
+++ b/source/index.ts
@@ -1,10 +1,14 @@
-import { DOMRenderer, VNode } from 'dom-renderer';
+import { DOMRenderer, DataObject, VNode } from 'dom-renderer';
 import { autorun } from 'mobx';
+import { CustomElement, isHTMLElementClass } from 'web-utility';
 
-interface ComponentMeta extends ElementDefinitionOptions {
+export interface ComponentMeta extends ElementDefinitionOptions {
     tagName: string;
 }
 
+/**
+ * Class decorator of Web components
+ */
 export function component({ tagName, ...meta }: ComponentMeta) {
     return <T extends CustomElementConstructor>(
         Class: T,
@@ -35,18 +39,65 @@ export function component({ tagName, ...meta }: ComponentMeta) {
     };
 }
 
-export function observer<T extends CustomElementConstructor>(
-    Class: T,
-    _: ClassDecoratorContext
-) {
-    class ObserverComponent extends (Class as CustomElementConstructor) {
+export type FunctionComponent<P extends DataObject = {}> = (props: P) => VNode;
+export type FC<P extends DataObject = {}> = FunctionComponent<P>;
+
+function wrapFunction<P>(func: FC<P>) {
+    return (props: P) => {
+        var tree: VNode,
+            renderer = new DOMRenderer();
+
+        const disposer = autorun(() => {
+            const newTree = func(props);
+
+            tree = tree ? renderer.patch(tree, newTree) : newTree;
+        });
+        const { unRef } = tree;
+
+        tree.unRef = node => (disposer(), unRef?.(node));
+
+        return tree;
+    };
+}
+
+export type ClassComponent = CustomElementConstructor;
+
+function wrapClass<T extends ClassComponent>(Class: T) {
+    class ObserverComponent
+        extends (Class as ClassComponent)
+        implements CustomElement
+    {
+        protected disposers = [];
+
         constructor() {
             super();
 
             const { update } = Object.getPrototypeOf(this);
             // @ts-ignore
-            this.update = () => autorun(() => update.call(this));
+            this.update = () =>
+                this.disposers.push(autorun(() => update.call(this)));
+        }
+
+        disconnectedCallback() {
+            for (const disposer of this.disposers) disposer();
         }
     }
     return ObserverComponent as unknown as T;
 }
+
+export type WebCellComponent = FunctionComponent | ClassComponent;
+
+/**
+ * Class decorator of Web components for MobX
+ */
+export function observer<T extends WebCellComponent>(
+    func: T,
+    _: ClassDecoratorContext
+): T;
+export function observer<T extends WebCellComponent>(func: T): T;
+export function observer<T extends WebCellComponent>(
+    func: T,
+    _?: ClassDecoratorContext
+) {
+    return isHTMLElementClass(func) ? wrapClass(func) : wrapFunction(func);
+}