implement wait-for-element (to be accessable in DOM)

wv-window.rkt

@@ -132,10 +132,22 @@
             (set! elem (new cl [window this] [element-id id]))
             (hash-set! element-hash id elem))
           )
-        (displayln (format "element ~a: ~a" id elem))
+        ;(displayln (format "element ~a: ~a" id elem))
         elem
         )
       )
+
+    (define (wait-for-element id)
+      (webview-call-js wv (string-append
+                           (format "{ let el = document.getElementById('~a');" id)
+                           "  while (el === null) { "
+                           "    window.setTimeout(function (){ }, 0);"
+                           (format "    el = document.getElementById('~a');" id)
+                           "  }"
+                           "  return true;"
+                           "}")
+                       )
+      )
         
     (define (connect! id type event callback)
       (let ((elem (element id type)))