make the eval consistent with function definition

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)

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")
 }

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.

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() {

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")
 

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) {

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
 }
 

page_eval.go

@@ -26,31 +26,22 @@ 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.
 	UserGesture bool
 }
 
 // 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