diff --git a/browser_test.go b/browser_test.go
index 096a8b03..7ea0faf5 100644
--- a/browser_test.go
+++ b/browser_test.go
@@ -163,7 +163,7 @@ func (t T) BrowserWaitEvent() {
 func (t T) BrowserCrash() {
 	browser := rod.New().Context(t.Context()).MustConnect()
 	page := browser.MustPage()
-	js := `new Promise(r => setTimeout(r, 10000))`
+	js := `() => new Promise(r => setTimeout(r, 10000))`
 
 	go t.Panic(func() {
 		page.MustEval(js)
diff --git a/dev_helpers_test.go b/dev_helpers_test.go
index 935b45d1..43ae8cc4 100644
--- a/dev_helpers_test.go
+++ b/dev_helpers_test.go
@@ -93,5 +93,5 @@ func (t T) ExposeHelpers() {
 	p := t.newPage(t.srcFile("fixtures/click.html"))
 	p.ExposeHelpers(js.ElementR)
 
-	t.Eq(p.MustElementByJS(`rod.elementR('button', 'click me')`).MustText(), "click me")
+	t.Eq(p.MustElementByJS(`() => rod.elementR('button', 'click me')`).MustText(), "click me")
 }
diff --git a/element.go b/element.go
index b270818c..f2b004e9 100644
--- a/element.go
+++ b/element.go
@@ -58,7 +58,7 @@ func (el *Element) Focus() error {
 		return err
 	}
 
-	_, err = el.Evaluate(Eval(`this.focus()`).ByUser())
+	_, err = el.Evaluate(Eval(`() => this.focus()`).ByUser())
 	return err
 }
 
@@ -143,7 +143,7 @@ func (el *Element) Tap() error {
 // The cursor can be mouse, finger, stylus, etc.
 // If not interactable err will be ErrNotInteractable, such as when covered by a modal,
 func (el *Element) Interactable() (pt *proto.Point, err error) {
-	noPointerEvents, err := el.Eval(`getComputedStyle(this).pointerEvents === 'none'`)
+	noPointerEvents, err := el.Eval(`() => getComputedStyle(this).pointerEvents === 'none'`)
 	if err != nil {
 		return nil, err
 	}
@@ -167,7 +167,7 @@ func (el *Element) Interactable() (pt *proto.Point, err error) {
 		return
 	}
 
-	scroll, err := el.page.root.Eval(`{ x: window.scrollX, y: window.scrollY }`)
+	scroll, err := el.page.root.Eval(`() => ({ x: window.scrollX, y: window.scrollY })`)
 	if err != nil {
 		return
 	}
@@ -302,7 +302,7 @@ func (el *Element) InputTime(t time.Time) error {
 
 // Blur is similar to the method Blur
 func (el *Element) Blur() error {
-	_, err := el.Evaluate(Eval("this.blur()").ByUser())
+	_, err := el.Evaluate(Eval("() => this.blur()").ByUser())
 	return err
 }
 
@@ -591,14 +591,14 @@ func (el *Element) WaitVisible() error {
 // Doc for readonly: https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/readonly
 func (el *Element) WaitEnabled() error {
 	defer el.tryTrace(TraceTypeWait, "enabled")()
-	return el.Wait(Eval(`!this.disabled`))
+	return el.Wait(Eval(`() => !this.disabled`))
 }
 
 // WaitWritable until the element is not readonly.
 // Doc for disabled: https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/disabled
 func (el *Element) WaitWritable() error {
 	defer el.tryTrace(TraceTypeWait, "writable")()
-	return el.Wait(Eval(`!this.readonly`))
+	return el.Wait(Eval(`() => !this.readonly`))
 }
 
 // WaitInvisible until the element invisible
@@ -633,7 +633,7 @@ func (el *Element) Resource() ([]byte, error) {
 
 // BackgroundImage returns the css background-image of the element
 func (el *Element) BackgroundImage() ([]byte, error) {
-	res, err := el.Eval(`window.getComputedStyle(this).backgroundImage.replace(/^url\("/, '').replace(/"\)$/, '')`)
+	res, err := el.Eval(`() => window.getComputedStyle(this).backgroundImage.replace(/^url\("/, '').replace(/"\)$/, '')`)
 	if err != nil {
 		return nil, err
 	}
@@ -684,7 +684,7 @@ func (el *Element) Release() error {
 
 // Remove the element from the page
 func (el *Element) Remove() error {
-	_, err := el.Eval(`this.remove()`)
+	_, err := el.Eval(`() => this.remove()`)
 	if err != nil {
 		return err
 	}
@@ -696,9 +696,9 @@ func (el *Element) Call(ctx context.Context, sessionID, methodName string, param
 	return el.page.Call(ctx, sessionID, methodName, params)
 }
 
-// Eval js on the page. For more info check the Element.Evaluate
+// Eval is a shortcut for Element.Evaluate with AwaitPromise, ByValue and AutoExp set to true.
 func (el *Element) Eval(js string, params ...interface{}) (*proto.RuntimeRemoteObject, error) {
-	return el.Evaluate(Eval(js, params...))
+	return el.Evaluate(Eval(js, params...).ByPromise())
 }
 
 // Evaluate is just a shortcut of Page.Evaluate with This set to current element.
diff --git a/element_test.go b/element_test.go
index 18429596..e860f882 100644
--- a/element_test.go
+++ b/element_test.go
@@ -177,9 +177,9 @@ func (t T) WaitInteractable() {
 func (t T) Hover() {
 	p := t.page.MustNavigate(t.srcFile("fixtures/click.html"))
 	el := p.MustElement("button")
-	el.MustEval(`this.onmouseenter = () => this.dataset['a'] = 1`)
+	el.MustEval(`() => this.onmouseenter = () => this.dataset['a'] = 1`)
 	el.MustHover()
-	t.Eq("1", el.MustEval(`this.dataset['a']`).String())
+	t.Eq("1", el.MustEval(`() => this.dataset['a']`).String())
 
 	t.mc.stubErr(1, proto.DOMScrollIntoViewIfNeeded{})
 	t.Err(el.Hover())
@@ -197,7 +197,7 @@ func (t T) Hover() {
 func (t T) ElementMoveMouseOut() {
 	p := t.page.MustNavigate(t.srcFile("fixtures/click.html"))
 	btn := p.MustElement("button")
-	btn.MustEval(`this.onmouseout = () => this.setAttribute('name', 'mouse moved.')`)
+	btn.MustEval(`() => this.onmouseout = () => this.setAttribute('name', 'mouse moved.')`)
 	t.Eq("mouse moved.", *btn.MustHover().MustMoveMouseOut().MustAttribute("name"))
 
 	t.mc.stubErr(1, proto.DOMGetContentQuads{})
@@ -227,7 +227,7 @@ func (t T) Iframes() {
 	el := frame02.MustElement("button")
 	el.MustClick()
 
-	t.Eq(frame01.MustEval(`testIsolation()`).Str(), "ok")
+	t.Eq(frame01.MustEval(`() => testIsolation()`).Str(), "ok")
 	t.True(frame02.MustHas("[a=ok]"))
 }
 
@@ -429,7 +429,7 @@ func (t T) SelectQuery() {
 	err := el.Select([]string{`[value="c"]`}, true, rod.SelectorTypeCSSSector)
 	t.E(err)
 
-	t.Eq(2, el.MustEval("this.selectedIndex").Int())
+	t.Eq(2, el.MustEval("() => this.selectedIndex").Int())
 }
 
 func (t T) SelectOptions() {
@@ -520,7 +520,7 @@ func (t T) SetFiles() {
 		slash("fixtures/alert.html"),
 	)
 
-	list := el.MustEval("Array.from(this.files).map(f => f.name)").Arr()
+	list := el.MustEval("() => Array.from(this.files).map(f => f.name)").Arr()
 	t.Len(list, 2)
 	t.Eq("alert.html", list[1].String())
 }
@@ -544,9 +544,9 @@ func (t T) WaitInvisible() {
 
 	go func() {
 		utils.Sleep(0.03)
-		h4.MustEval(`this.remove()`)
+		h4.MustEval(`() => this.remove()`)
 		utils.Sleep(0.03)
-		btn.MustEval(`this.style.visibility = 'hidden'`)
+		btn.MustEval(`() => this.style.visibility = 'hidden'`)
 	}()
 
 	h4.MustWaitInvisible()
@@ -568,7 +568,7 @@ func (t T) WaitWritable() {
 func (t T) WaitStable() {
 	p := t.page.MustNavigate(t.srcFile("fixtures/wait-stable.html"))
 	el := p.MustElement("button")
-	el.MustEval(`this.classList.add("play")`)
+	el.MustEval(`() => this.classList.add("play")`)
 	start := time.Now()
 	el.MustWaitStable()
 	t.Gt(time.Since(start), time.Second)
@@ -596,7 +596,7 @@ func (t T) WaitStable() {
 func (t T) WaitStableRAP() {
 	p := t.page.MustNavigate(t.srcFile("fixtures/wait-stable.html"))
 	el := p.MustElement("button")
-	el.MustEval(`this.classList.add("play")`)
+	el.MustEval(`() => this.classList.add("play")`)
 	start := time.Now()
 	t.E(el.WaitStableRAF())
 	t.Gt(time.Since(start), time.Second)
@@ -723,7 +723,7 @@ func (t T) FnErr() {
 	t.True(errors.As(err, &e))
 	t.Eq(proto.RuntimeRemoteObjectSubtypeError, e.Exception.Subtype)
 
-	_, err = el.ElementByJS(rod.Eval("foo()"))
+	_, err = el.ElementByJS(rod.Eval("() => foo()"))
 	t.Err(err)
 	t.Has(err.Error(), "ReferenceError: foo is not defined")
 	t.True(errors.Is(err, &rod.ErrEval{}))
@@ -749,9 +749,9 @@ func (t T) ElementOthers() {
 	el.MustScrollIntoView()
 	t.Eq("submit", el.MustElement("[type=submit]").MustText())
 	t.Eq("<input type=\"submit\" value=\"submit\">", el.MustElement("[type=submit]").MustHTML())
-	el.MustWait(`true`)
-	t.Eq("form", el.MustElementByJS(`this`).MustDescribe().LocalName)
-	t.Len(el.MustElementsByJS(`[]`), 0)
+	el.MustWait(`() => true`)
+	t.Eq("form", el.MustElementByJS(`() => this`).MustDescribe().LocalName)
+	t.Len(el.MustElementsByJS(`() => []`), 0)
 }
 
 func (t T) ElementEqual() {
diff --git a/examples_test.go b/examples_test.go
index 12357f5f..8a6a85d5 100644
--- a/examples_test.go
+++ b/examples_test.go
@@ -43,13 +43,13 @@ func Example() {
 	fmt.Println("Found", len(page.MustElements("input")), "input elements")
 
 	// Eval js on the page
-	page.MustEval(`console.log("hello world")`)
+	page.MustEval(`() => console.log("hello world")`)
 
 	// Pass parameters as json objects to the js function. This MustEval will result 3
 	fmt.Println("1 + 2 =", page.MustEval(`(a, b) => a + b`, 1, 2).Int())
 
 	// When eval on an element, "this" in the js is the current DOM element.
-	fmt.Println(page.MustElement("title").MustEval(`this.innerText`).String())
+	fmt.Println(page.MustElement("title").MustEval(`() => this.innerText`).String())
 
 	// Output:
 	// Git is the most widely used version control system.
@@ -433,7 +433,7 @@ func Example_handle_events() {
 		}
 	}
 
-	page.MustEval(`console.log("hello", "world")`)
+	page.MustEval(`() => console.log("hello", "world")`)
 
 	<-done
 
@@ -483,7 +483,7 @@ func Example_hijack_requests() {
 
 	go router.Run()
 
-	browser.MustPage("https://go-rod.github.io").MustWait(`document.title === 'hi'`)
+	browser.MustPage("https://go-rod.github.io").MustWait(`() => document.title === 'hi'`)
 
 	fmt.Println("done")
 
@@ -494,7 +494,7 @@ func Example_hijack_requests() {
 func Example_eval_reuse_remote_object() {
 	page := rod.New().MustConnect().MustPage()
 
-	fn := page.MustEvaluate(rod.Eval(`Math.random`).ByObject())
+	fn := page.MustEvaluate(rod.Eval(`() => Math.random`).ByObject())
 
 	res := page.MustEval(`f => f()`, fn)
 
@@ -580,7 +580,7 @@ func Example_load_extension() {
 
 	page := rod.New().ControlURL(u).MustConnect().MustPage("http://mdn.dev")
 
-	page.MustWait(`document.title === 'test-extension'`)
+	page.MustWait(`() => document.title === 'test-extension'`)
 
 	fmt.Println("ok")
 
diff --git a/hijack_test.go b/hijack_test.go
index b014475f..6292ede1 100644
--- a/hijack_test.go
+++ b/hijack_test.go
@@ -213,7 +213,7 @@ func (t T) HijackFailRequest() {
 
 	t.page.MustNavigate(s.URL("/page")).MustWaitLoad()
 
-	t.page.MustWait(`document.title === 'Failed to fetch'`)
+	t.page.MustWait(`() => document.title === 'Failed to fetch'`)
 
 	{ // test error log
 		t.mc.stub(1, proto.FetchFailRequest{}, func(send StubSend) (gson.JSON, error) {
diff --git a/page.go b/page.go
index 368229ac..b73437bb 100644
--- a/page.go
+++ b/page.go
@@ -173,14 +173,14 @@ func (p *Page) Navigate(url string) error {
 // NavigateBack history.
 func (p *Page) NavigateBack() error {
 	// Not using cdp API because it doesn't work for iframe
-	_, err := p.Evaluate(Eval(`history.back()`).ByUser())
+	_, err := p.Evaluate(Eval(`() => history.back()`).ByUser())
 	return err
 }
 
 // NavigateForward history.
 func (p *Page) NavigateForward() error {
 	// Not using cdp API because it doesn't work for iframe
-	_, err := p.Evaluate(Eval(`history.forward()`).ByUser())
+	_, err := p.Evaluate(Eval(`() => history.forward()`).ByUser())
 	return err
 }
 
@@ -194,7 +194,7 @@ func (p *Page) Reload() error {
 	})
 
 	// Not using cdp API because it doesn't work for iframe
-	_, err := p.Evaluate(Eval(`location.reload()`).ByUser())
+	_, err := p.Evaluate(Eval(`() => location.reload()`).ByUser())
 	if err != nil {
 		return err
 	}
@@ -542,7 +542,7 @@ func (p *Page) WaitIdle(timeout time.Duration) (err error) {
 // Doc: https://developer.mozilla.org/en-US/docs/Web/API/window/requestAnimationFrame
 func (p *Page) WaitRepaint() error {
 	// we use root here because iframe doesn't trigger requestAnimationFrame
-	_, err := p.root.Eval(`new Promise(r => requestAnimationFrame(r))`)
+	_, err := p.root.Eval(`() => new Promise(r => requestAnimationFrame(r))`)
 	return err
 }
 
diff --git a/page_eval.go b/page_eval.go
index 5d3900ea..b6ed4492 100644
--- a/page_eval.go
+++ b/page_eval.go
@@ -26,20 +26,15 @@ type EvalOptions struct {
 	// ThisObj represents the "this" object in the JS
 	ThisObj *proto.RuntimeRemoteObject
 
-	// JS code to eval. It can be an expression or function definition. If it's a function definition
-	// the function will be executed with the JSArgs. Such as
-	//     1 + 2
-	// is the same as
-	//     () => 1 + 2
-	// or
-	//     function() {
-	//         return 1 + 2
-	//     }
+	// JS function definition to execute.
 	JS string
 
-	// JSArgs represents the arguments in the JS if the JS is a function definition.
+	// JSArgs represents the arguments that will be passed to JS.
 	// If an argument is *proto.RuntimeRemoteObject type, the corresponding remote object will be used.
 	// Or it will be passed as a plain JSON value.
+	// When an arg in the args is a *js.Function, the arg will be cached on the page's js context.
+	// When the arg.Name exists in the page's cache, it reuse the cache without sending the definition to the browser again.
+	// Useful when you need to eval a huge js expression many times.
 	JSArgs []interface{}
 
 	// Whether execution should be treated as initiated by user in the UI.
@@ -47,10 +42,6 @@ type EvalOptions struct {
 }
 
 // Eval creates a EvalOptions with ByValue set to true.
-//
-// When an arg in the args is a *js.Function, the arg will be cached on the page's js context.
-// When the arg.Name exists in the page's cache, it reuse the cache without sending the definition to the browser again.
-// Useful when you need to eval a huge js expression many times.
 func Eval(js string, args ...interface{}) *EvalOptions {
 	return &EvalOptions{
 		ByValue:      true,
@@ -66,7 +57,7 @@ func evalHelper(fn *js.Function, args ...interface{}) *EvalOptions {
 	return &EvalOptions{
 		ByValue: true,
 		JSArgs:  append([]interface{}{fn}, args...),
-		JS:      `(f, ...args) => f.apply(this, args)`,
+		JS:      `function (f, ...args) { return f.apply(this, args) }`,
 	}
 }
 
@@ -119,15 +110,12 @@ func (e *EvalOptions) ByPromise() *EvalOptions {
 
 func (e *EvalOptions) formatToJSFunc() string {
 	js := strings.TrimSpace(e.JS)
-	if detectJSFunction(js) {
-		return fmt.Sprintf(`function() { return (%s).apply(this, arguments) }`, js)
-	}
-	return fmt.Sprintf(`function() { return %s }`, js)
+	return fmt.Sprintf(`function() { return (%s).apply(this, arguments) }`, js)
 }
 
-// Eval is just a shortcut for Page.Evaluate with AwaitPromise set true.
-func (p *Page) Eval(js string, jsArgs ...interface{}) (*proto.RuntimeRemoteObject, error) {
-	return p.Evaluate(Eval(js, jsArgs...).ByPromise())
+// Eval is a shortcut for Page.Evaluate with AwaitPromise, ByValue set to true.
+func (p *Page) Eval(js string, args ...interface{}) (*proto.RuntimeRemoteObject, error) {
+	return p.Evaluate(Eval(js, args...).ByPromise())
 }
 
 // Evaluate js on the page.
@@ -202,13 +190,12 @@ func (p *Page) Expose(name string, fn func(gson.JSON) (interface{}, error)) (sto
 		return
 	}
 
-	code := fmt.Sprintf(`(%s)("%s", "%s")`, js.ExposeFunc.Definition, name, bind)
-
-	_, err = p.Evaluate(Eval(code))
+	_, err = p.Evaluate(Eval(js.ExposeFunc.Definition, name, bind))
 	if err != nil {
 		return
 	}
 
+	code := fmt.Sprintf(`(%s)("%s", "%s")`, js.ExposeFunc.Definition, name, bind)
 	remove, err := p.EvalOnNewDocument(code)
 	if err != nil {
 		return
diff --git a/page_eval_test.go b/page_eval_test.go
index 18ac4319..2c7bbfb5 100644
--- a/page_eval_test.go
+++ b/page_eval_test.go
@@ -18,7 +18,7 @@ func (t T) PageEvalOnNewDocument() {
 	// to activate the script
 	p.MustNavigate(t.blank())
 
-	t.Eq(p.MustEval("rod").String(), "ok")
+	t.Eq(p.MustEval("() => rod").String(), "ok")
 
 	t.Panic(func() {
 		t.mc.stubErr(1, proto.PageAddScriptToEvaluateOnNewDocument{})
@@ -32,19 +32,13 @@ func (t T) PageEval() {
 	t.Eq(3, page.MustEval(`
 		(a, b) => a + b
 	`, 1, 2).Int())
-	t.Eq(10, page.MustEval(`
-		10
-	`).Int())
-	t.Eq(1, page.MustEval(`a => 1`).Int())
-	t.Eq(1, page.MustEval(`function() { return 1 }`).Int())
-	t.Eq(1, page.MustEval(`((1))`).Int())
-	t.Neq(1, page.MustEval(`a = () => 1`).Int())
-	t.Neq(1, page.MustEval(`a = function() { return 1 }`))
-	t.Neq(1, page.MustEval(`/* ) */`))
 
 	// reuse obj
 	obj := page.MustEvaluate(rod.Eval(`() => () => 'ok'`).ByObject())
 	t.Eq("ok", page.MustEval(`f => f()`, obj).Str())
+
+	_, err := page.Eval(`10`)
+	t.Has(err.Error(), `eval js error: TypeError: 10.apply is not a function`)
 }
 
 func (t T) PageEvaluateRetry() {
@@ -56,7 +50,7 @@ func (t T) PageEvaluateRetry() {
 		})
 		return gson.New(nil), cdp.ErrCtxNotFound
 	})
-	t.Eq(1, page.MustEval(`1`).Int())
+	t.Eq(1, page.MustEval(`() => 1`).Int())
 }
 
 func (t T) PageUpdateJSCtxIDErr() {
@@ -66,7 +60,7 @@ func (t T) PageUpdateJSCtxIDErr() {
 		t.mc.stubErr(1, proto.RuntimeEvaluate{})
 		return gson.New(nil), cdp.ErrCtxNotFound
 	})
-	t.Err(page.Eval(`1`))
+	t.Err(page.Eval(`() => 1`))
 
 	frame := page.MustElement("iframe").MustFrame()
 
@@ -87,16 +81,16 @@ func (t T) PageExpose() {
 	})
 
 	utils.All(func() {
-		res := page.MustEval(`exposedFunc({k: 'a'})`)
+		res := page.MustEval(`() => exposedFunc({k: 'a'})`)
 		t.Eq("a", res.Str())
 	}, func() {
-		res := page.MustEval(`exposedFunc({k: 'b'})`)
+		res := page.MustEval(`() => exposedFunc({k: 'b'})`)
 		t.Eq("b", res.Str())
 	})()
 
 	// survive the reload
 	page.MustReload().MustWaitLoad()
-	res := page.MustEval(`exposedFunc({k: 'ok'})`)
+	res := page.MustEval(`() => exposedFunc({k: 'ok'})`)
 	t.Eq("ok", res.Str())
 
 	stop()
@@ -105,7 +99,7 @@ func (t T) PageExpose() {
 		stop()
 	})
 	t.Panic(func() {
-		page.MustReload().MustWaitLoad().MustEval(`exposedFunc()`)
+		page.MustReload().MustWaitLoad().MustEval(`() => exposedFunc()`)
 	})
 	t.Panic(func() {
 		t.mc.stubErr(1, proto.RuntimeCallFunctionOn{})
@@ -122,7 +116,7 @@ func (t T) PageExpose() {
 }
 
 func (t T) Release() {
-	res, err := t.page.Evaluate(rod.Eval(`document`).ByObject())
+	res, err := t.page.Evaluate(rod.Eval(`() => document`).ByObject())
 	t.E(err)
 	t.page.MustRelease(res)
 }
@@ -136,7 +130,7 @@ func (t T) PromiseLeak() {
 	p := t.page.MustNavigate(t.blank())
 
 	utils.All(func() {
-		_, err := p.Eval(`new Promise(r => setTimeout(() => r(location.href), 1000))`)
+		_, err := p.Eval(`() => new Promise(r => setTimeout(() => r(location.href), 1000))`)
 		t.Is(err, cdp.ErrCtxDestroyed)
 	}, func() {
 		utils.Sleep(0.3)
@@ -151,7 +145,7 @@ func (t T) ObjectLeak() {
 
 	p := t.page.MustNavigate(t.blank())
 
-	obj := p.MustEvaluate(rod.Eval("{a:1}").ByObject())
+	obj := p.MustEvaluate(rod.Eval("() => ({a:1})").ByObject())
 	p.MustReload().MustWaitLoad()
 	t.Panic(func() {
 		p.MustEvaluate(rod.Eval(`obj => obj`, obj))
@@ -189,9 +183,9 @@ func (t T) ConcurrentEval() {
 
 	start := time.Now()
 	utils.All(func() {
-		list <- p.MustEval(`new Promise(r => setTimeout(r, 1000, 2))`).Int()
+		list <- p.MustEval(`() => new Promise(r => setTimeout(r, 1000, 2))`).Int()
 	}, func() {
-		list <- p.MustEval(`new Promise(r => setTimeout(r, 500, 1))`).Int()
+		list <- p.MustEval(`() => new Promise(r => setTimeout(r, 500, 1))`).Int()
 	})()
 	duration := time.Since(start)
 
@@ -220,11 +214,11 @@ func (t T) PageIframeReload() {
 
 func (t T) PageObjCrossNavigation() {
 	p := t.page.MustNavigate(t.blank())
-	obj := p.MustEvaluate(rod.Eval(`{}`).ByObject())
+	obj := p.MustEvaluate(rod.Eval(`() => ({})`).ByObject())
 
 	t.page.MustNavigate(t.blank())
 
-	_, err := p.Evaluate(rod.Eval(`1`).This(obj))
+	_, err := p.Evaluate(rod.Eval(`() => 1`).This(obj))
 	t.Is(err, &rod.ErrObjectNotFound{})
 	t.Has(err.Error(), "cannot find object: {\"type\":\"object\"")
 }
@@ -240,5 +234,5 @@ func (t T) EvalOptionsString() {
 	p := t.page.MustNavigate(t.srcFile("fixtures/click.html"))
 	el := p.MustElement("button")
 
-	t.Eq(rod.Eval(`this.parentElement`).This(el.Object).String(), "this.parentElement() button")
+	t.Eq(rod.Eval(`() => this.parentElement`).This(el.Object).String(), "() => this.parentElement() button")
 }
diff --git a/page_test.go b/page_test.go
index f30f06be..858a6f64 100644
--- a/page_test.go
+++ b/page_test.go
@@ -146,7 +146,7 @@ func (t T) PageCloseCancel() {
 	}()
 	t.Eq(page.Close().Error(), "page close canceled")
 
-	page.MustEval(`window.onbeforeunload = null`)
+	page.MustEval(`() => window.onbeforeunload = null`)
 	page.MustClose()
 }
 
@@ -159,7 +159,7 @@ func (t T) DisableDomain() {
 }
 
 func (t T) PageContext() {
-	t.page.Timeout(time.Hour).CancelTimeout().MustEval(`1`)
+	t.page.Timeout(time.Hour).CancelTimeout().MustEval(`() => 1`)
 }
 
 func (t T) PageActivate() {
@@ -186,8 +186,8 @@ func (t T) Window() {
 	page.MustWindowMinimize()
 	page.MustWindowNormal()
 	page.MustSetWindow(0, 0, 1211, 611)
-	t.Eq(1211, page.MustEval(`window.innerWidth`).Int())
-	t.Eq(611, page.MustEval(`window.innerHeight`).Int())
+	t.Eq(1211, page.MustEval(`() => window.innerWidth`).Int())
+	t.Eq(611, page.MustEval(`() => window.innerHeight`).Int())
 
 	t.Panic(func() {
 		t.mc.stubErr(1, proto.BrowserGetWindowForTarget{})
@@ -206,12 +206,12 @@ func (t T) Window() {
 func (t T) SetViewport() {
 	page := t.newPage(t.blank())
 	page.MustSetViewport(317, 419, 0, false)
-	res := page.MustEval(`[window.innerWidth, window.innerHeight]`)
+	res := page.MustEval(`() => [window.innerWidth, window.innerHeight]`)
 	t.Eq(317, res.Get("0").Int())
 	t.Eq(419, res.Get("1").Int())
 
 	page2 := t.newPage(t.blank())
-	res = page2.MustEval(`[window.innerWidth, window.innerHeight]`)
+	res = page2.MustEval(`() => [window.innerWidth, window.innerHeight]`)
 	t.Neq(int(317), res.Get("0").Int())
 }
 
@@ -271,7 +271,7 @@ func (t T) SetDocumentContent() {
 func (t T) EmulateDevice() {
 	page := t.newPage(t.blank())
 	page.MustEmulate(devices.IPhone6or7or8)
-	res := page.MustEval(`[window.innerWidth, window.innerHeight, navigator.userAgent]`)
+	res := page.MustEval(`() => [window.innerWidth, window.innerHeight, navigator.userAgent]`)
 
 	// TODO: this seems like a bug of chromium
 	{
@@ -304,14 +304,14 @@ func (t T) PageCloseErr() {
 func (t T) PageAddScriptTag() {
 	p := t.page.MustNavigate(t.blank()).MustWaitLoad()
 
-	res := p.MustAddScriptTag(t.srcFile("fixtures/add-script-tag.js")).MustEval(`count()`)
+	res := p.MustAddScriptTag(t.srcFile("fixtures/add-script-tag.js")).MustEval(`() => count()`)
 	t.Eq(0, res.Int())
 
-	res = p.MustAddScriptTag(t.srcFile("fixtures/add-script-tag.js")).MustEval(`count()`)
+	res = p.MustAddScriptTag(t.srcFile("fixtures/add-script-tag.js")).MustEval(`() => count()`)
 	t.Eq(1, res.Int())
 
 	t.E(p.AddScriptTag("", `let ok = 'yes'`))
-	res = p.MustEval(`ok`)
+	res = p.MustEval(`() => ok`)
 	t.Eq("yes", res.String())
 }
 
@@ -319,14 +319,14 @@ func (t T) PageAddStyleTag() {
 	p := t.page.MustNavigate(t.srcFile("fixtures/click.html")).MustWaitLoad()
 
 	res := p.MustAddStyleTag(t.srcFile("fixtures/add-style-tag.css")).
-		MustElement("h4").MustEval(`getComputedStyle(this).color`)
+		MustElement("h4").MustEval(`() => getComputedStyle(this).color`)
 	t.Eq("rgb(255, 0, 0)", res.String())
 
 	p.MustAddStyleTag(t.srcFile("fixtures/add-style-tag.css"))
 	t.Len(p.MustElements("link"), 1)
 
 	t.E(p.AddStyleTag("", "h4 { color: green; }"))
-	res = p.MustElement("h4").MustEval(`getComputedStyle(this).color`)
+	res = p.MustElement("h4").MustEval(`() => getComputedStyle(this).color`)
 	t.Eq("rgb(0, 128, 0)", res.String())
 }
 
@@ -340,12 +340,12 @@ func (t T) PageWaitOpen() {
 	newPage := wait()
 	defer newPage.MustClose()
 
-	t.Eq("new page", newPage.MustEval("window.a").String())
+	t.Eq("new page", newPage.MustEval("() => window.a").String())
 }
 
 func (t T) PageWait() {
 	page := t.page.MustNavigate(t.srcFile("fixtures/click.html"))
-	page.MustWait(`document.querySelector('button') !== null`)
+	page.MustWait(`() => document.querySelector('button') !== null`)
 
 	t.Panic(func() {
 		t.mc.stubErr(1, proto.RuntimeCallFunctionOn{})
@@ -561,7 +561,7 @@ func (t T) MouseDrag() {
 	mouse.MustUp("left")
 
 	utils.Sleep(0.3)
-	t.Eq(page.MustEval(`dragTrack`).Str(), " move 3 3 down 3 3 move 22 28 move 41 54 move 60 80 up 60 80")
+	t.Eq(page.MustEval(`() => dragTrack`).Str(), " move 3 3 down 3 3 move 22 28 move 41 54 move 60 80 up 60 80")
 }
 
 func (t T) NativeDrag(got.Skip) { // devtools doesn't support to use mouse event to simulate it for now
@@ -601,7 +601,7 @@ func (t T) Touch() {
 	p.MoveTo(50, 60)
 	touch.MustMove(p).MustCancel()
 
-	page.MustWait(`touchTrack == ' start 10 20 end start 30 40 end start 30 40 move 50 60 cancel'`)
+	page.MustWait(`() => touchTrack == ' start 10 20 end start 30 40 end start 30 40 move 50 60 cancel'`)
 
 	t.Panic(func() {
 		t.mc.stubErr(1, proto.InputDispatchTouchEvent{})
@@ -635,12 +635,12 @@ func (t T) ScreenshotFullPage() {
 	data := p.MustScreenshotFullPage()
 	img, err := png.Decode(bytes.NewBuffer(data))
 	t.E(err)
-	res := p.MustEval(`({w: document.documentElement.scrollWidth, h: document.documentElement.scrollHeight})`)
+	res := p.MustEval(`() => ({w: document.documentElement.scrollWidth, h: document.documentElement.scrollHeight})`)
 	t.Eq(res.Get("w").Int(), img.Bounds().Dx())
 	t.Eq(res.Get("h").Int(), img.Bounds().Dy())
 
 	// after the full page screenshot the window size should be the same as before
-	res = p.MustEval(`({w: innerWidth, h: innerHeight})`)
+	res = p.MustEval(`() => ({w: innerWidth, h: innerHeight})`)
 	t.Eq(1280, res.Get("w").Int())
 	t.Eq(800, res.Get("h").Int())
 
@@ -707,14 +707,14 @@ func (t T) PageScroll() {
 	p.Mouse.MustScroll(100, 190)
 	t.E(p.Mouse.Scroll(200, 300, 5))
 
-	p.MustWait(`pageXOffset > 200 && pageYOffset > 300`)
+	p.MustWait(`() => pageXOffset > 200 && pageYOffset > 300`)
 }
 
 func (t T) PageConsoleLog() {
 	p := t.newPage(t.blank()).MustWaitLoad()
 	e := &proto.RuntimeConsoleAPICalled{}
 	wait := p.WaitEvent(e)
-	p.MustEval(`console.log(1, {b: ['test']})`)
+	p.MustEval(`() => console.log(1, {b: ['test']})`)
 	wait()
 	t.Eq("test", p.MustObjectToJSON(e.Args[1]).Get("b.0").String())
 	t.Eq(`1 map[b:[test]]`, p.MustObjectsToJSON(e.Args).Join(" "))
diff --git a/query.go b/query.go
index e6bc9fb8..07da9dea 100644
--- a/query.go
+++ b/query.go
@@ -89,7 +89,7 @@ func (ps Pages) Find(selector string) (*Page, error) {
 // FindByURL returns the page that has the url that matches the jsRegex
 func (ps Pages) FindByURL(jsRegex string) (*Page, error) {
 	for _, page := range ps {
-		res, err := page.Eval(`location.href`)
+		res, err := page.Eval(`() => location.href`)
 		if err != nil {
 			return nil, err
 		}
@@ -493,7 +493,7 @@ func (el *Element) ElementByJS(opts *EvalOptions) (*Element, error) {
 
 // Parent returns the parent element in the DOM tree
 func (el *Element) Parent() (*Element, error) {
-	return el.ElementByJS(Eval(`this.parentElement`))
+	return el.ElementByJS(Eval(`() => this.parentElement`))
 }
 
 // Parents that match the selector
@@ -503,12 +503,12 @@ func (el *Element) Parents(selector string) (Elements, error) {
 
 // Next returns the next sibling element in the DOM tree
 func (el *Element) Next() (*Element, error) {
-	return el.ElementByJS(Eval(`this.nextElementSibling`))
+	return el.ElementByJS(Eval(`() => this.nextElementSibling`))
 }
 
 // Previous returns the previous sibling element in the DOM tree
 func (el *Element) Previous() (*Element, error) {
-	return el.ElementByJS(Eval(`this.previousElementSibling`))
+	return el.ElementByJS(Eval(`() => this.previousElementSibling`))
 }
 
 // Elements returns all elements that match the css selector
diff --git a/query_test.go b/query_test.go
index ad3fa28e..ec0dcfb1 100644
--- a/query_test.go
+++ b/query_test.go
@@ -172,9 +172,9 @@ func (t T) PageRace() {
 	p.Race().ElementR("button", "02").MustHandle(func(e *rod.Element) { t.Eq("02", e.MustText()) }).MustDo()
 	t.Eq("02", p.Race().ElementR("button", "02").MustDo().MustText())
 
-	p.Race().MustElementByJS("document.querySelector('button')", nil).
+	p.Race().MustElementByJS("() => document.querySelector('button')", nil).
 		MustHandle(func(e *rod.Element) { t.Eq("01", e.MustText()) }).MustDo()
-	t.Eq("01", p.Race().MustElementByJS("document.querySelector('button')", nil).MustDo().MustText())
+	t.Eq("01", p.Race().MustElementByJS("() => document.querySelector('button')", nil).MustDo().MustText())
 
 	el, err := p.Sleeper(func() utils.Sleeper { return utils.CountSleeper(2) }).Race().
 		Element("not-exists").MustHandle(func(e *rod.Element) {}).
@@ -184,7 +184,7 @@ func (t T) PageRace() {
 	t.Err(err)
 	t.Nil(el)
 
-	el, err = p.Race().MustElementByJS(`notExists()`, nil).Do()
+	el, err = p.Race().MustElementByJS(`() => notExists()`, nil).Do()
 	t.Err(err)
 	t.Nil(el)
 }
@@ -194,9 +194,9 @@ func (t T) PageRaceRetryInHandle() {
 	p.Race().Element("div").MustHandle(func(e *rod.Element) {
 		go func() {
 			utils.Sleep(0.5)
-			e.MustElement("button").MustEval(`this.innerText = '04'`)
+			e.MustElement("button").MustEval(`() => this.innerText = '04'`)
 		}()
-		e.MustElement("button").MustWait("this.innerText === '04'")
+		e.MustElement("button").MustWait("() => this.innerText === '04'")
 	}).MustDo()
 }
 
@@ -254,7 +254,7 @@ func (t T) ElementsFromElement() {
 func (t T) ElementParent() {
 	p := t.page.MustNavigate(t.srcFile("fixtures/input.html"))
 	el := p.MustElement("input").MustParent()
-	t.Eq("FORM", el.MustEval(`this.tagName`).String())
+	t.Eq("FORM", el.MustEval(`() => this.tagName`).String())
 }
 
 func (t T) ElementParents() {
@@ -300,9 +300,9 @@ func (t T) ElementTracing() {
 func (t T) PageElementByJS() {
 	p := t.page.MustNavigate(t.srcFile("fixtures/click.html"))
 
-	t.Eq(p.MustElementByJS(`document.querySelector('button')`).MustText(), "click me")
+	t.Eq(p.MustElementByJS(`() => document.querySelector('button')`).MustText(), "click me")
 
-	_, err := p.ElementByJS(rod.Eval(`1`))
+	_, err := p.ElementByJS(rod.Eval(`() => 1`))
 	t.Is(err, &rod.ErrExpectElement{})
 	t.Eq(err.Error(), "expect js to return an element, but got: {\"type\":\"number\",\"value\":1,\"description\":\"1\"}")
 }
@@ -310,18 +310,18 @@ func (t T) PageElementByJS() {
 func (t T) PageElementsByJS() {
 	p := t.page.MustNavigate(t.srcFile("fixtures/selector.html")).MustWaitLoad()
 
-	t.Len(p.MustElementsByJS("document.querySelectorAll('button')"), 4)
+	t.Len(p.MustElementsByJS("() => document.querySelectorAll('button')"), 4)
 
-	_, err := p.ElementsByJS(rod.Eval(`[1]`))
+	_, err := p.ElementsByJS(rod.Eval(`() => [1]`))
 	t.Is(err, &rod.ErrExpectElements{})
 	t.Eq(err.Error(), "expect js to return an array of elements, but got: {\"type\":\"number\",\"value\":1,\"description\":\"1\"}")
-	_, err = p.ElementsByJS(rod.Eval(`1`))
+	_, err = p.ElementsByJS(rod.Eval(`() => 1`))
 	t.Eq(err.Error(), "expect js to return an array of elements, but got: {\"type\":\"number\",\"value\":1,\"description\":\"1\"}")
-	_, err = p.ElementsByJS(rod.Eval(`foo()`))
+	_, err = p.ElementsByJS(rod.Eval(`() => foo()`))
 	t.Err(err)
 
 	t.mc.stubErr(1, proto.RuntimeGetProperties{})
-	_, err = p.ElementsByJS(rod.Eval(`[document.body]`))
+	_, err = p.ElementsByJS(rod.Eval(`() => [document.body]`))
 	t.Err(err)
 
 	t.mc.stubErr(4, proto.RuntimeCallFunctionOn{})
diff --git a/utils.go b/utils.go
index a04480d7..65547e85 100644
--- a/utils.go
+++ b/utils.go
@@ -286,53 +286,6 @@ func mustToJSONForDev(value interface{}) string {
 	return buf.String()
 }
 
-// detect if a js string is a function definition
-var regFn = regexp.MustCompile(`\A\s*function\s*\(`)
-
-// detect if a js string is a function definition
-// Samples:
-//
-// function () {}
-// a => {}
-// (a, b, c) =>
-// ({a: b}, ...list) => {}
-func detectJSFunction(js string) bool {
-	if regFn.MatchString(js) {
-		return true
-	}
-
-	// The algorithm is pretty simple, the braces before "=>" must be balanced.
-	// Such as "foo(() => {})", there are 2 "(", but only 1 ")".
-	// Here we use a simple state machine.
-
-	balanced := true
-	last := ' '
-	for _, r := range js {
-		if r == '(' {
-			if balanced {
-				balanced = false
-			} else {
-				return false
-			}
-		}
-		if r == ')' {
-			if balanced {
-				return false
-			}
-			balanced = true
-		}
-
-		if last == '=' {
-			if r == '>' {
-				return balanced
-			}
-			return false
-		}
-		last = r
-	}
-	return false
-}
-
 // https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs
 var regDataURI = regexp.MustCompile(`\Adata:(.+?)?(;base64)?,`)