Add basic locator support

We now support creating a locator using one of page.locator and
frame.locator. This commit adds a simple unit test to verify whether we
can create locators using the mentioned methods. However, the test is
not that useful, we can remove it later when we add integration tests.

api/frame.go

@@ -52,6 +52,8 @@ type Frame interface {
 	IsVisible(selector string, opts goja.Value) bool
 	ID() string
 	LoaderID() string
+	// Locator creates and returns a new locator for this frame.
+	Locator(selector string, opts goja.Value) Locator
 	Name() string
 	Query(selector string) ElementHandle
 	QueryAll(selector string) []ElementHandle

api/locator.go

@@ -0,0 +1,4 @@
+package api
+
+// Locator represents a way to find element(s) on a page at any moment.
+type Locator interface{}

api/page.go

@@ -61,6 +61,8 @@ type Page interface {
 	IsEnabled(selector string, opts goja.Value) bool
 	IsHidden(selector string, opts goja.Value) bool
 	IsVisible(selector string, opts goja.Value) bool
+	// Locator creates and returns a new locator for this page (main frame).
+	Locator(selector string, opts goja.Value) Locator
 	MainFrame() Frame
 	Opener() Page
 	Pause()

common/frame.go

@@ -1249,6 +1249,13 @@ func (f *Frame) ID() string {
 	return f.id.String()
 }
 
+// Locator creates and returns a new locator for this frame.
+func (f *Frame) Locator(selector string, opts goja.Value) api.Locator {
+	f.log.Debugf("Frame:Locator", "fid:%s furl:%q selector:%q opts:%+v", f.ID(), f.URL(), selector, opts)
+
+	return NewLocator(f.ctx, selector, f, f.log)
+}
+
 // LoaderID returns the ID of the frame that loaded this frame.
 func (f *Frame) LoaderID() string {
 	f.propertiesMu.RLock()

common/locator.go

@@ -0,0 +1,25 @@
+package common
+
+import (
+	"context"
+)
+
+// Locator represent a way to find element(s) on the page at any moment.
+type Locator struct {
+	selector string
+
+	frame *Frame
+
+	ctx context.Context
+	log *Logger
+}
+
+// NewLocator creates and returns a new locator.
+func NewLocator(ctx context.Context, selector string, f *Frame, l *Logger) *Locator {
+	return &Locator{
+		selector: selector,
+		frame:    f,
+		ctx:      ctx,
+		log:      l,
+	}
+}

common/page.go

@@ -615,6 +615,13 @@ func (p *Page) IsVisible(selector string, opts goja.Value) bool {
 	return p.MainFrame().IsVisible(selector, opts)
 }
 
+// Locator creates and returns a new locator for this page (main frame).
+func (p *Page) Locator(selector string, opts goja.Value) api.Locator {
+	p.logger.Debugf("Page:Locator", "sid:%s sel: %q opts:%+v", p.sessionID(), selector, opts)
+
+	return p.MainFrame().Locator(selector, opts)
+}
+
 // MainFrame returns the main frame on the page.
 func (p *Page) MainFrame() api.Frame {
 	mf := p.frameManager.MainFrame()

common/page_test.go

@@ -0,0 +1,31 @@
+package common
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// TestPageLocator can be removed later on when we add integration
+// tests. Since we don't yet have any of them, it makes sense to keep
+// this test.
+func TestPageLocator(t *testing.T) {
+	const (
+		wantMainFrameID = "1"
+		wantSelector    = "span"
+	)
+	ctx := context.TODO()
+	p := &Page{
+		ctx: ctx,
+		frameManager: &FrameManager{
+			ctx:       ctx,
+			mainFrame: &Frame{id: wantMainFrameID, ctx: ctx},
+		},
+	}
+	l := p.Locator(wantSelector, nil).(*Locator) //nolint:forcetypeassert
+	assert.Equal(t, wantSelector, l.selector)
+	assert.Equal(t, wantMainFrameID, string(l.frame.id))
+
+	// other behavior will be tested via integration tests
+}