Feature/#33 wait class function (#63)

* #33 Lib cleanup. Added WAIT_CLASS and WAIT_CLASS_ALL functions

* #33 Fixed attr update

* #33 HTMLElement.WaitForClass

* #33 Updated HTMLDocument.WaitForClass

pkg/stdlib/html/wait_element.go

@@ -0,0 +1,51 @@
+package html
+
+import (
+	"context"
+	"github.com/MontFerret/ferret/pkg/runtime/core"
+	"github.com/MontFerret/ferret/pkg/runtime/values"
+	"github.com/MontFerret/ferret/pkg/stdlib/html/driver/dynamic"
+)
+
+/*
+ * Waits for element to appear in the DOM.
+ * Stops the execution until it finds an element or operation times out.
+ * @param doc (HTMLDocument) - Dynamic HTMLDocument.
+ * @param selector (String) - Target element's selector.
+ * @param timeout (Int, optional) - Optional timeout. Default 5000 ms.
+ */
+func WaitElement(_ context.Context, args ...core.Value) (core.Value, error) {
+	err := core.ValidateArgs(args, 2, 3)
+
+	if err != nil {
+		return values.None, err
+	}
+
+	arg := args[0]
+	selector := args[1].String()
+	timeout := values.NewInt(defaultTimeout)
+
+	if len(args) > 2 {
+		err = core.ValidateType(args[2], core.IntType)
+
+		if err != nil {
+			return values.None, err
+		}
+
+		timeout = args[2].(values.Int)
+	}
+
+	err = core.ValidateType(arg, core.HTMLDocumentType)
+
+	if err != nil {
+		return values.None, err
+	}
+
+	doc, ok := arg.(*dynamic.HTMLDocument)
+
+	if !ok {
+		return values.None, core.Errors(core.ErrInvalidType, ErrNotDynamic)
+	}
+
+	return values.None, doc.WaitForSelector(values.NewString(selector), timeout)
+}