fix alert box blocking (#89)

* fix alert box blocking

fix bug #71

* Update fix in full screen case

fix bug  #71

chrome/chrome.go

@@ -8,6 +8,7 @@ import (
 	"net/url"
 	"strings"
 	"time"
+	"fmt"
 
 	"github.com/chromedp/cdproto/emulation"
 	"github.com/chromedp/cdproto/page"
@@ -153,10 +154,24 @@ func (chrome *Chrome) Screenshot(url *url.URL) ([]byte, error) {
 
 	if chrome.FullPage {
 		// straight from: https://github.com/chromedp/examples/blob/255873ca0d76b00e0af8a951a689df3eb4f224c3/screenshot/main.go#L54
+		chromedp.ListenTarget(ctx, func(ev interface{}) {
+			if ev, ok := ev.(*page.EventJavascriptDialogOpening); ok {
+				fmt.Println("closing alert:", ev.Message)
+				go func() {
+					if err := chromedp.Run(ctx,
+						page.HandleJavaScriptDialog(true),
+					); err != nil {
+						panic(err)
+					}
+				}()
+			}
+		})
 		if err := chromedp.Run(ctx, chromedp.Tasks{
 			chromedp.Navigate(url.String()),
 			chromedp.Sleep(time.Duration(chrome.Delay) * time.Second),
 			chromedp.ActionFunc(func(ctx context.Context) error {
+
+
 				// get layout metrics
 				_, _, contentSize, err := page.GetLayoutMetrics().Do(ctx)
 				if err != nil {
@@ -197,6 +212,18 @@ func (chrome *Chrome) Screenshot(url *url.URL) ([]byte, error) {
 
 	} else {
 		// normal viewport screenshot
+		chromedp.ListenTarget(ctx, func(ev interface{}) {
+			if ev, ok := ev.(*page.EventJavascriptDialogOpening); ok {
+				fmt.Println("closing alert:", ev.Message)
+				go func() {
+					if err := chromedp.Run(ctx,
+						page.HandleJavaScriptDialog(true),
+					); err != nil {
+						panic(err)
+					}
+				}()
+			}
+		})
 		if err := chromedp.Run(ctx, chromedp.Tasks{
 			chromedp.Navigate(url.String()),
 			chromedp.Sleep(time.Duration(chrome.Delay) * time.Second),