add events

Author: arutyunyan

src/frontend/example/TodoList.php

@@ -21,7 +21,11 @@ class="form-control"
                         .'>
                     <button
                         type="button"
-                        class="btn btn-primary">
+                        class="btn btn-primary"'.
+                        $this->event('onclick', function () {
+                            return $this->setState(['task' => null]);
+                        })
+                        .'>
                         <i class="bi bi-plus"></i>
                     </button>
                 </div>

src/frontend/html/component/Component.php

@@ -42,6 +42,9 @@ public function setState($obj)
     {
         $s = [];
         foreach ($obj as $prop => $value) {
+            if (is_null($value)) {
+                $value = "null";
+            }
             $s[] = "$prop:$value";
         }
         return $this->className().'.setState({'.implode(',', $s).'})';
@@ -144,6 +147,11 @@ public function inputValue($name)
         return ' id="'.$id.'"';
     }
 
+    public function event($event, $callback)
+    {
+        return $event.'="'.$callback().'"';
+    }
+
     public function range($start, $end, $callback)
     {
         $str = '';