Add keypress event to todo example (#241)

* add enter keypress event in todo example

* fix linting

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

pyscriptjs/examples/todo.py

@@ -12,6 +12,10 @@ new_task_content = Element("new-task-content")
 
 
 def add_task(*ags, **kws):
+    # ignore empty task
+    if not new_task_content.element.value:
+        return None
+
     # create task
     task_id = f"task-{len(tasks)}"
     task = {
@@ -44,3 +48,6 @@ def add_task(*ags, **kws):
 def add_task_event(e):
     if e.key == "Enter":
         add_task()
+
+
+new_task_content.element.onkeypress = add_task_event