Add the implementation to parse the options

This copies the parsing logic from the existing browserContext.waitFor
Event() into the new WaitForEventOptions type's parse method. It also
modifies it so that the data that is parsed is updated in the type and
during parsing it will return an error instead of panicking.

common/browser_context_options.go

@@ -3,6 +3,7 @@ package common
 import (
 	"context"
 	"fmt"
+	"reflect"
 	"time"
 
 	"github.com/grafana/xk6-browser/k6ext"
@@ -153,5 +154,32 @@ func NewWaitForEventOptions(defaultTimeout time.Duration) *WaitForEventOptions {
 // It can parse only a callable predicate function or an object
 // which contains a callable predicate function and a timeout.
 func (w *WaitForEventOptions) Parse(ctx context.Context, optsOrPredicate goja.Value) error {
+	var (
+		isCallable bool
+	)
+	if gojaValueExists(optsOrPredicate) {
+		switch optsOrPredicate.ExportType() {
+		case reflect.TypeOf(goja.Object{}):
+			rt := k6ext.Runtime(ctx)
+			opts := optsOrPredicate.ToObject(rt)
+			for _, k := range opts.Keys() {
+				switch k {
+				case "predicate":
+					w.PredicateFn, isCallable = goja.AssertFunction(opts.Get(k))
+					if !isCallable {
+						return fmt.Errorf("predicate function is not callable")
+					}
+				case "timeout":
+					w.Timeout = time.Duration(opts.Get(k).ToInteger()) * time.Millisecond
+				}
+			}
+		default:
+			w.PredicateFn, isCallable = goja.AssertFunction(optsOrPredicate)
+			if !isCallable {
+				return fmt.Errorf("predicate function is not callable")
+			}
+		}
+	}
+
 	return nil
 }