From 00f6cfbd285d6baa24bf7b5fb407bf5fa77d0cfd Mon Sep 17 00:00:00 2001
From: "Nicholas H.Tollervey" <ntoll@ntoll.org>
Date: Mon, 31 Mar 2025 13:14:52 +0100
Subject: [PATCH] A more refined Event class, with additional tests.

---
 core/src/stdlib/pyscript.js            |  2 +-
 core/src/stdlib/pyscript/events.py     | 81 ++++++++++++++++++++++----
 core/tests/index.html                  |  2 +-
 core/tests/python/tests/test_events.py | 57 ++++++++++++++++++
 4 files changed, 128 insertions(+), 14 deletions(-)

diff --git a/core/src/stdlib/pyscript.js b/core/src/stdlib/pyscript.js
index 3c4ea4f9..a042bfb1 100644
--- a/core/src/stdlib/pyscript.js
+++ b/core/src/stdlib/pyscript.js
@@ -3,7 +3,7 @@ export default {
   "pyscript": {
     "__init__.py": "from polyscript import lazy_py_modules as py_import\nfrom pyscript.magic_js import RUNNING_IN_WORKER,PyWorker,config,current_target,document,js_import,js_modules,sync,window\nfrom pyscript.display import HTML,display\nfrom pyscript.fetch import fetch\nfrom pyscript.storage import Storage,storage\nfrom pyscript.websocket import WebSocket\nfrom pyscript.events import when,Event\nif not RUNNING_IN_WORKER:from pyscript.workers import create_named_worker,workers",
     "display.py": "_L='_repr_mimebundle_'\n_K='image/svg+xml'\n_J='application/json'\n_I='__repr__'\n_H='savefig'\n_G='text/html'\n_F='image/jpeg'\n_E='application/javascript'\n_D='utf-8'\n_C='text/plain'\n_B='image/png'\n_A=None\nimport base64,html,io,re\nfrom pyscript.magic_js import current_target,document,window\n_MIME_METHODS={_H:_B,'_repr_javascript_':_E,'_repr_json_':_J,'_repr_latex':'text/latex','_repr_png_':_B,'_repr_jpeg_':_F,'_repr_pdf_':'application/pdf','_repr_svg_':_K,'_repr_markdown_':'text/markdown','_repr_html_':_G,_I:_C}\ndef _render_image(mime,value,meta):\n\tA=value\n\tif isinstance(A,bytes):A=base64.b64encode(A).decode(_D)\n\tB=re.compile('^([A-Za-z0-9+/]{4})*([A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{2}==)?$')\n\tif len(A)>0 and not B.match(A):A=base64.b64encode(A.encode(_D)).decode(_D)\n\tC=f\"data:{mime};charset=utf-8;base64,{A}\";D=' '.join(['{k}=\"{v}\"'for(A,B)in meta.items()]);return f'<img src=\"{C}\" {D}></img>'\ndef _identity(value,meta):return value\n_MIME_RENDERERS={_C:html.escape,_G:_identity,_B:lambda value,meta:_render_image(_B,value,meta),_F:lambda value,meta:_render_image(_F,value,meta),_K:_identity,_J:_identity,_E:lambda value,meta:f\"<script>{value}<\\\\/script>\"}\nclass HTML:\n\tdef __init__(A,html):A._html=html\n\tdef _repr_html_(A):return A._html\ndef _eval_formatter(obj,print_method):\n\tB=obj;A=print_method\n\tif A==_I:return repr(B)\n\tif hasattr(B,A):\n\t\tif A==_H:C=io.BytesIO();B.savefig(C,format='png');C.seek(0);return base64.b64encode(C.read()).decode(_D)\n\t\treturn getattr(B,A)()\n\tif A==_L:return{},{}\ndef _format_mime(obj):\n\tC=obj\n\tif isinstance(C,str):return html.escape(C),_C\n\tD=_eval_formatter(C,_L)\n\tif isinstance(D,tuple):E,I=D\n\telse:E=D\n\tA,F=_A,[]\n\tfor(H,B)in _MIME_METHODS.items():\n\t\tif B in E:A=E[B]\n\t\telse:A=_eval_formatter(C,H)\n\t\tif A is _A:continue\n\t\tif B not in _MIME_RENDERERS:F.append(B);continue\n\t\tbreak\n\tif A is _A:\n\t\tif F:window.console.warn(f\"Rendered object requested unavailable MIME renderers: {F}\")\n\t\tA=repr(A);B=_C\n\telif isinstance(A,tuple):A,G=A\n\telse:G={}\n\treturn _MIME_RENDERERS[B](A,G),B\ndef _write(element,value,append=False):\n\tB=element;C,D=_format_mime(value)\n\tif C=='\\\\n':return\n\tif append:A=document.createElement('div');B.append(A)\n\telse:\n\t\tA=B.lastElementChild\n\t\tif A is _A:A=B\n\tif D in(_E,_G):E=document.createRange().createContextualFragment(C);A.append(E)\n\telse:A.innerHTML=C\ndef display(*E,target=_A,append=True):\n\tD=append;A=target\n\tif A is _A:A=current_target()\n\telif not isinstance(A,str):C=f\"target must be str or None, not {A.__class__.__name__}\";raise TypeError(C)\n\telif A=='':C='Cannot have an empty target';raise ValueError(C)\n\telif A.startswith('#'):A=A[1:]\n\tB=document.getElementById(A)\n\tif B is _A:C=f\"Invalid selector with id={A}. Cannot be found in the page.\";raise ValueError(C)\n\tif B.tagName=='SCRIPT'and hasattr(B,'target'):B=B.target\n\tfor F in E:\n\t\tif not D:B.replaceChildren()\n\t\t_write(B,F,append=D)",
-    "events.py": "import asyncio,inspect,sys\nfrom functools import wraps\nfrom pyscript.magic_js import document\nfrom pyscript.ffi import create_proxy\nfrom pyscript.util import is_awaitable\nfrom pyscript import config\nclass Event:\n\tdef __init__(A):A._listeners=[]\n\tdef trigger(C,result):\n\t\tB=result\n\t\tfor A in C._listeners:\n\t\t\tif is_awaitable(A):asyncio.create_task(A(B))\n\t\t\telse:A(B)\n\tdef add_listener(B,listener):\n\t\tA=listener\n\t\tif is_awaitable(A)or callable(A):\n\t\t\tif A not in B._listeners:B._listeners.append(A)\n\t\telse:C='Listener must be callable or awaitable.';raise ValueError(C)\n\tdef remove_listener(A,*B):\n\t\tif B:\n\t\t\tfor C in B:A._listeners.remove(C)\n\t\telse:A._listeners=[]\ndef when(target,*B,**D):\n\tG='handler';C=target;E=None\n\tif B and(callable(B[0])or is_awaitable(B[0])):E=B[0]\n\telif callable(D.get(G))or is_awaitable(D.get(G)):E=D.pop(G)\n\tif isinstance(C,str):\n\t\tA=B[0]if B else D.pop('selector')\n\t\tif not A:I='No selector provided.';raise ValueError(I)\n\t\tfrom pyscript.web import Element as J,ElementCollection as K\n\t\tif isinstance(A,str):F=document.querySelectorAll(A)\n\t\telif isinstance(A,J):F=[A._dom_element]\n\t\telif isinstance(A,K):F=[A._dom_element for A in A]\n\t\telse:F=A if isinstance(A,list)else[A]\n\tdef H(func):\n\t\tE='positional arguments';D='takes';A=func\n\t\tif config['type']=='mpy':\n\t\t\tif is_awaitable(A):\n\t\t\t\tasync def B(*C,**F):\n\t\t\t\t\ttry:return await A(*C,**F)\n\t\t\t\t\texcept TypeError as B:\n\t\t\t\t\t\tif D in str(B)and E in str(B):return await A()\n\t\t\t\t\t\traise\n\t\t\telse:\n\t\t\t\tdef B(*C,**F):\n\t\t\t\t\ttry:return A(*C,**F)\n\t\t\t\t\texcept TypeError as B:\n\t\t\t\t\t\tif D in str(B)and E in str(B):return A()\n\t\t\t\t\t\traise\n\t\telse:\n\t\t\tG=inspect.signature(A)\n\t\t\tif G.parameters:\n\t\t\t\tif is_awaitable(A):\n\t\t\t\t\tasync def B(event):return await A(event)\n\t\t\t\telse:B=A\n\t\t\telif is_awaitable(A):\n\t\t\t\tasync def B(*B,**C):return await A()\n\t\t\telse:\n\t\t\t\tdef B(*B,**C):return A()\n\t\tB=wraps(A)(B)\n\t\tif isinstance(C,Event):C.add_listener(B)\n\t\telif isinstance(C,list)and all(isinstance(A,Event)for A in C):\n\t\t\tfor H in C:H.add_listener(B)\n\t\telse:\n\t\t\tfor I in F:I.addEventListener(C,create_proxy(B))\n\t\treturn B\n\treturn H(E)if E else H",
+    "events.py": "import asyncio,inspect\nfrom functools import wraps\nfrom pyscript.magic_js import document\nfrom pyscript.ffi import create_proxy\nfrom pyscript.util import is_awaitable\nfrom pyscript import config\nclass Event:\n\tdef __init__(A):A._listeners=[];A._result=None;A._triggered=False\n\t@property\n\tdef triggered(self):return self._triggered\n\t@property\n\tdef result(self):\n\t\tif self.triggered:return self._result\n\t\tA='Event has not been triggered yet. No result available.';raise ValueError(A)\n\tdef trigger(A,result=None):\n\t\tif A.triggered:B='Event has already been triggered.';raise RuntimeError(B)\n\t\tA._triggered=True;A._result=result\n\t\tfor C in A._listeners:A._call_listener(C)\n\tdef add_listener(B,listener):\n\t\tA=listener\n\t\tif is_awaitable(A)or callable(A):\n\t\t\tif A not in B._listeners:\n\t\t\t\tB._listeners.append(A)\n\t\t\t\tif B.triggered:B._call_listener(A)\n\t\telse:C='Listener must be callable or awaitable.';raise ValueError(C)\n\tdef remove_listener(A,*B):\n\t\tif B:\n\t\t\tfor C in B:A._listeners.remove(C)\n\t\telse:A._listeners=[]\n\tdef _call_listener(B,listener):\n\t\tA=listener\n\t\tif is_awaitable(A):asyncio.create_task(A(B._result))\n\t\telse:A(B._result)\ndef when(target,*B,**D):\n\tG='handler';C=target;E=None\n\tif B and(callable(B[0])or is_awaitable(B[0])):E=B[0]\n\telif callable(D.get(G))or is_awaitable(D.get(G)):E=D.pop(G)\n\tif isinstance(C,str):\n\t\tA=B[0]if B else D.pop('selector')\n\t\tif not A:I='No selector provided.';raise ValueError(I)\n\t\tfrom pyscript.web import Element as J,ElementCollection as K\n\t\tif isinstance(A,str):F=document.querySelectorAll(A)\n\t\telif isinstance(A,J):F=[A._dom_element]\n\t\telif isinstance(A,K):F=[A._dom_element for A in A]\n\t\telse:F=A if isinstance(A,list)else[A]\n\tdef H(func):\n\t\tE='positional arguments';D='takes';A=func\n\t\tif config['type']=='mpy':\n\t\t\tif is_awaitable(A):\n\t\t\t\tasync def B(*C,**F):\n\t\t\t\t\ttry:return await A(*C,**F)\n\t\t\t\t\texcept TypeError as B:\n\t\t\t\t\t\tif D in str(B)and E in str(B):return await A()\n\t\t\t\t\t\traise\n\t\t\telse:\n\t\t\t\tdef B(*C,**F):\n\t\t\t\t\ttry:return A(*C,**F)\n\t\t\t\t\texcept TypeError as B:\n\t\t\t\t\t\tif D in str(B)and E in str(B):return A()\n\t\t\t\t\t\traise\n\t\telse:\n\t\t\tG=inspect.signature(A)\n\t\t\tif G.parameters:\n\t\t\t\tif is_awaitable(A):\n\t\t\t\t\tasync def B(event):return await A(event)\n\t\t\t\telse:B=A\n\t\t\telif is_awaitable(A):\n\t\t\t\tasync def B(*B,**C):return await A()\n\t\t\telse:\n\t\t\t\tdef B(*B,**C):return A()\n\t\tB=wraps(A)(B)\n\t\tif isinstance(C,Event):C.add_listener(B)\n\t\telif isinstance(C,list)and all(isinstance(A,Event)for A in C):\n\t\t\tfor H in C:H.add_listener(B)\n\t\telse:\n\t\t\tfor I in F:I.addEventListener(C,create_proxy(B))\n\t\treturn B\n\treturn H(E)if E else H",
     "fetch.py": "import json,js\nfrom pyscript.util import as_bytearray\nclass _Response:\n\tdef __init__(A,response):A._response=response\n\tdef __getattr__(A,attr):return getattr(A._response,attr)\n\tasync def arrayBuffer(B):\n\t\tA=await B._response.arrayBuffer()\n\t\tif hasattr(A,'to_py'):return A.to_py()\n\t\treturn memoryview(as_bytearray(A))\n\tasync def blob(A):return await A._response.blob()\n\tasync def bytearray(A):B=await A._response.arrayBuffer();return as_bytearray(B)\n\tasync def json(A):return json.loads(await A.text())\n\tasync def text(A):return await A._response.text()\nclass _DirectResponse:\n\t@staticmethod\n\tdef setup(promise,response):A=promise;A._response=_Response(response);return A._response\n\tdef __init__(B,promise):A=promise;B._promise=A;A._response=None;A.arrayBuffer=B.arrayBuffer;A.blob=B.blob;A.bytearray=B.bytearray;A.json=B.json;A.text=B.text\n\tasync def _response(A):\n\t\tif not A._promise._response:await A._promise\n\t\treturn A._promise._response\n\tasync def arrayBuffer(A):B=await A._response();return await B.arrayBuffer()\n\tasync def blob(A):B=await A._response();return await B.blob()\n\tasync def bytearray(A):B=await A._response();return await B.bytearray()\n\tasync def json(A):B=await A._response();return await B.json()\n\tasync def text(A):B=await A._response();return await B.text()\ndef fetch(url,**B):C=js.JSON.parse(json.dumps(B));D=lambda response,*B:_DirectResponse.setup(A,response);A=js.fetch(url,C).then(D);_DirectResponse(A);return A",
     "ffi.py": "try:\n\timport js;from pyodide.ffi import create_proxy as _cp,to_js as _py_tjs;from_entries=js.Object.fromEntries\n\tdef _tjs(value,**A):\n\t\tB='dict_converter'\n\t\tif not hasattr(A,B):A[B]=from_entries\n\t\treturn _py_tjs(value,**A)\nexcept:from jsffi import create_proxy as _cp;from jsffi import to_js as _tjs\ncreate_proxy=_cp\nto_js=_tjs",
     "flatted.py": "import json as _json\nclass _Known:\n\tdef __init__(A):A.key=[];A.value=[]\nclass _String:\n\tdef __init__(A,value):A.value=value\ndef _array_keys(value):\n\tA=[];B=0\n\tfor C in value:A.append(B);B+=1\n\treturn A\ndef _object_keys(value):\n\tA=[]\n\tfor B in value:A.append(B)\n\treturn A\ndef _is_array(value):return isinstance(value,(list,tuple))\ndef _is_object(value):return isinstance(value,dict)\ndef _is_string(value):return isinstance(value,str)\ndef _index(known,input,value):B=value;A=known;input.append(B);C=str(len(input)-1);A.key.append(B);A.value.append(C);return C\ndef _loop(keys,input,known,output):\n\tA=output\n\tfor B in keys:\n\t\tC=A[B]\n\t\tif isinstance(C,_String):_ref(B,input[int(C.value)],input,known,A)\n\treturn A\ndef _ref(key,value,input,known,output):\n\tB=known;A=value\n\tif _is_array(A)and A not in B:B.append(A);A=_loop(_array_keys(A),input,B,A)\n\telif _is_object(A)and A not in B:B.append(A);A=_loop(_object_keys(A),input,B,A)\n\toutput[key]=A\ndef _relate(known,input,value):\n\tB=known;A=value\n\tif _is_string(A)or _is_array(A)or _is_object(A):\n\t\ttry:return B.value[B.key.index(A)]\n\t\texcept:return _index(B,input,A)\n\treturn A\ndef _transform(known,input,value):\n\tB=known;A=value\n\tif _is_array(A):\n\t\tC=[]\n\t\tfor F in A:C.append(_relate(B,input,F))\n\t\treturn C\n\tif _is_object(A):\n\t\tD={}\n\t\tfor E in A:D[E]=_relate(B,input,A[E])\n\t\treturn D\n\treturn A\ndef _wrap(value):\n\tA=value\n\tif _is_string(A):return _String(A)\n\tif _is_array(A):\n\t\tB=0\n\t\tfor D in A:A[B]=_wrap(D);B+=1\n\telif _is_object(A):\n\t\tfor C in A:A[C]=_wrap(A[C])\n\treturn A\ndef parse(value,*C,**D):\n\tA=value;E=_json.loads(A,*C,**D);B=[]\n\tfor A in E:B.append(_wrap(A))\n\tinput=[]\n\tfor A in B:\n\t\tif isinstance(A,_String):input.append(A.value)\n\t\telse:input.append(A)\n\tA=input[0]\n\tif _is_array(A):return _loop(_array_keys(A),input,[A],A)\n\tif _is_object(A):return _loop(_object_keys(A),input,[A],A)\n\treturn A\ndef stringify(value,*D,**E):\n\tB=_Known();input=[];C=[];A=int(_index(B,input,value))\n\twhile A<len(input):C.append(_transform(B,input,input[A]));A+=1\n\treturn _json.dumps(C,*D,**E)",
diff --git a/core/src/stdlib/pyscript/events.py b/core/src/stdlib/pyscript/events.py
index da3efacd..33ba755c 100644
--- a/core/src/stdlib/pyscript/events.py
+++ b/core/src/stdlib/pyscript/events.py
@@ -1,6 +1,5 @@
 import asyncio
 import inspect
-import sys
 
 from functools import wraps
 from pyscript.magic_js import document
@@ -11,38 +10,87 @@ from pyscript import config
 
 class Event:
     """
-    Represents something that may happen at some point in the future.
+    Events represent something that may happen at some point in time (usually
+    the future). They're used to coordinate code when the timing of an event is
+    not known in advance (e.g. a button click or a network response).
+
+    An event is triggered with an arbitrary result. If no result is given, then
+    None is assumed as the result.
+
+    Add listener functions to the event, to be called with the result when the
+    event is triggered. The listener functions can be callable or awaitable. If
+    the listener is added several times, it will be called only once.
+
+    If the event was triggered before a listener is added, the listener will be
+    called as soon as it is added, with the result of the event.
+
+    If the event is never triggered, then its listeners will never be called.
+    It's also possible to remove listeners from the event.
+
+    If the result of the event is not available, a ValueError will be raised
+    when trying to access the result property. A RuntimeError will be raised if
+    the event is triggered more than once.
     """
 
     def __init__(self):
+        # To contain the listeners to be called when the event is triggered.
         self._listeners = []
+        # The result associated with the event.
+        self._result = None
+        # A flag to indicate if the event has been triggered.
+        self._triggered = False
 
-    def trigger(self, result):
+    @property
+    def triggered(self):
         """
-        Trigger the event with a result to pass into the handlers.
+        A boolean flag to indicate if the event has been triggered.
         """
+        return self._triggered
+
+    @property
+    def result(self):
+        """
+        The result of the event.
+        """
+        if self.triggered:
+            return self._result
+        msg = "Event has not been triggered yet. No result available."
+        raise ValueError(msg)
+
+    def trigger(self, result=None):
+        """
+        Trigger the event with an arbitrary result to pass into the listeners.
+        An event may only be triggered once (otherwise a RuntimeError is
+        raised).
+        """
+        if self.triggered:
+            msg = "Event has already been triggered."
+            raise RuntimeError(msg)
+        self._triggered = True
+        self._result = result
         for listener in self._listeners:
-            if is_awaitable(listener):
-                # Use create task to avoid making this an async function.
-                asyncio.create_task(listener(result))
-            else:
-                listener(result)
+            self._call_listener(listener)
 
     def add_listener(self, listener):
         """
-        Add a callable/awaitable to listen to when this event is triggered.
+        Add a callable/awaitable that listens for the result, when this event
+        is triggered.
         """
         if is_awaitable(listener) or callable(listener):
             if listener not in self._listeners:
                 self._listeners.append(listener)
+                if self.triggered:
+                    # If the event was already triggered, call the listener
+                    # immediately with the result.
+                    self._call_listener(listener)
         else:
             msg = "Listener must be callable or awaitable."
             raise ValueError(msg)
 
     def remove_listener(self, *args):
         """
-        Clear the specified handler functions in *args. If no handlers
-        provided, clear all handlers.
+        Clear the specified listener functions in *args. If no listeners are
+        provided, clear all the listeners.
         """
         if args:
             for listener in args:
@@ -50,6 +98,15 @@ class Event:
         else:
             self._listeners = []
 
+    def _call_listener(self, listener):
+        """
+        Call the referenced listener with the event's result.
+        """
+        if is_awaitable(listener):
+            asyncio.create_task(listener(self._result))
+        else:
+            listener(self._result)
+
 
 def when(target, *args, **kwargs):
     """
diff --git a/core/tests/index.html b/core/tests/index.html
index 08ef0c69..b03d3832 100644
--- a/core/tests/index.html
+++ b/core/tests/index.html
@@ -14,5 +14,5 @@
             a:hover { opacity: 1; }
         </style>
     </head>
-    <body><ul><li><strong><span>javascript</span></strong><ul><li><a href="./javascript/async-listener.html">async-listener<small>.html</small></a></li><li><a href="./javascript/config-url.html">config-url<small>.html</small></a></li><li><a href="./javascript/config_type.html">config_type<small>.html</small></a></li><li><strong><a href="./javascript/fetch/index.html">fetch</a></strong></li><li><a href="./javascript/ffi.html">ffi<small>.html</small></a></li><li><a href="./javascript/hooks.html">hooks<small>.html</small></a></li><li><strong><a href="./javascript/issue-2093/index.html">issue-2093</a></strong></li><li><a href="./javascript/js-storage.html">js-storage<small>.html</small></a></li><li><a href="./javascript/js_modules.html">js_modules<small>.html</small></a></li><li><strong><a href="./javascript/loader/index.html">loader</a></strong></li><li><a href="./javascript/mpy-error.html">mpy-error<small>.html</small></a></li><li><a href="./javascript/mpy-no-error.html">mpy-no-error<small>.html</small></a></li><li><a href="./javascript/mpy.html">mpy<small>.html</small></a></li><li><a href="./javascript/py-terminal-main.html">py-terminal-main<small>.html</small></a></li><li><a href="./javascript/py-terminal-worker.html">py-terminal-worker<small>.html</small></a></li><li><a href="./javascript/py-terminal.html">py-terminal<small>.html</small></a></li><li><a href="./javascript/py-terminals.html">py-terminals<small>.html</small></a></li><li><strong><a href="./javascript/pyodide-cache/index.html">pyodide-cache</a></strong></li><li><strong><a href="./javascript/pyodide-lockfile/index.html">pyodide-lockfile</a></strong></li><li><a href="./javascript/storage.html">storage<small>.html</small></a></li><li><strong><span>workers</span></strong><ul><li><strong><a href="./javascript/workers/create_named/index.html">create_named</a></strong></li><li><strong><a href="./javascript/workers/mpy/index.html">mpy</a></strong></li><li><strong><a href="./javascript/workers/py/index.html">py</a></strong></li></ul></li></ul></li><li><strong><a href="./manual/index.html">manual</a></strong><ul><li><a href="./manual/all-done.html">all-done<small>.html</small></a></li><li><a href="./manual/async.html">async<small>.html</small></a></li><li><a href="./manual/camera.html">camera<small>.html</small></a></li><li><a href="./manual/click.html">click<small>.html</small></a></li><li><a href="./manual/code-a-part.html">code-a-part<small>.html</small></a></li><li><a href="./manual/combo.html">combo<small>.html</small></a></li><li><a href="./manual/config.html">config<small>.html</small></a></li><li><a href="./manual/create-element.html">create-element<small>.html</small></a></li><li><a href="./manual/dialog.html">dialog<small>.html</small></a></li><li><a href="./manual/display.html">display<small>.html</small></a></li><li><strong><a href="./manual/donkey/index.html">donkey</a></strong></li><li><a href="./manual/emoji.html">emoji<small>.html</small></a></li><li><a href="./manual/error.html">error<small>.html</small></a></li><li><strong><a href="./manual/fs/index.html">fs</a></strong></li><li><strong><a href="./manual/game/index.html">game</a></strong></li><li><a href="./manual/html-decode.html">html-decode<small>.html</small></a></li><li><a href="./manual/input.html">input<small>.html</small></a></li><li><a href="./manual/interpreter.html">interpreter<small>.html</small></a></li><li><strong><a href="./manual/issue-2228/index.html">issue-2228</a></strong></li><li><strong><a href="./manual/issue-2246/index.html">issue-2246</a></strong></li><li><strong><a href="./manual/issue-2302/index.html">issue-2302</a></strong></li><li><strong><a href="./manual/issue-2304/index.html">issue-2304</a></strong></li><li><strong><a href="./manual/issue-7015/index.html">issue-7015</a></strong></li><li><a href="./manual/multi.html">multi<small>.html</small></a></li><li><a href="./manual/multiple-editors.html">multiple-editors<small>.html</small></a></li><li><a href="./manual/no-error.html">no-error<small>.html</small></a></li><li><strong><a href="./manual/no_sab/index.html">no_sab</a></strong></li><li><strong><a href="./manual/piratical/index.html">piratical</a></strong></li><li><a href="./manual/py-editor.html">py-editor<small>.html</small></a></li><li><a href="./manual/py-editor-failure.html">py-editor-failure<small>.html</small></a></li><li><strong><a href="./manual/py-terminals/index.html">py-terminals</a></strong><ul><li><a href="./manual/py-terminals/no-repl.html">no-repl<small>.html</small></a></li><li><a href="./manual/py-terminals/repl.html">repl<small>.html</small></a></li></ul></li><li><a href="./manual/py_modules.html">py_modules<small>.html</small></a></li><li><strong><a href="./manual/service-worker/index.html">service-worker</a></strong></li><li><a href="./manual/split-config.html">split-config<small>.html</small></a></li><li><a href="./manual/submit.html">submit<small>.html</small></a></li><li><a href="./manual/target.html">target<small>.html</small></a></li><li><a href="./manual/test_display_HTML.html">test_display_HTML<small>.html</small></a></li><li><a href="./manual/test_when.html">test_when<small>.html</small></a></li><li><a href="./manual/worker.html">worker<small>.html</small></a></li></ul></li><li><strong><a href="./python/index.html">python</a></strong></li></ul></body>
+    <body><ul><li><strong><span>javascript</span></strong><ul><li><a href="./javascript/async-listener.html">async-listener<small>.html</small></a></li><li><a href="./javascript/config-url.html">config-url<small>.html</small></a></li><li><a href="./javascript/config_type.html">config_type<small>.html</small></a></li><li><strong><a href="./javascript/fetch/index.html">fetch</a></strong></li><li><a href="./javascript/ffi.html">ffi<small>.html</small></a></li><li><a href="./javascript/hooks.html">hooks<small>.html</small></a></li><li><strong><a href="./javascript/issue-2093/index.html">issue-2093</a></strong></li><li><a href="./javascript/js-storage.html">js-storage<small>.html</small></a></li><li><a href="./javascript/js_modules.html">js_modules<small>.html</small></a></li><li><strong><a href="./javascript/loader/index.html">loader</a></strong></li><li><a href="./javascript/media.html">media<small>.html</small></a></li><li><a href="./javascript/mpy-error.html">mpy-error<small>.html</small></a></li><li><a href="./javascript/mpy-no-error.html">mpy-no-error<small>.html</small></a></li><li><a href="./javascript/mpy.html">mpy<small>.html</small></a></li><li><a href="./javascript/py-terminal-main.html">py-terminal-main<small>.html</small></a></li><li><a href="./javascript/py-terminal-worker.html">py-terminal-worker<small>.html</small></a></li><li><a href="./javascript/py-terminal.html">py-terminal<small>.html</small></a></li><li><a href="./javascript/py-terminals.html">py-terminals<small>.html</small></a></li><li><strong><a href="./javascript/pyodide-cache/index.html">pyodide-cache</a></strong></li><li><strong><a href="./javascript/pyodide-lockfile/index.html">pyodide-lockfile</a></strong></li><li><a href="./javascript/storage.html">storage<small>.html</small></a></li><li><strong><span>workers</span></strong><ul><li><strong><a href="./javascript/workers/create_named/index.html">create_named</a></strong></li><li><strong><a href="./javascript/workers/mpy/index.html">mpy</a></strong></li><li><strong><a href="./javascript/workers/py/index.html">py</a></strong></li></ul></li></ul></li><li><strong><a href="./manual/index.html">manual</a></strong><ul><li><a href="./manual/all-done.html">all-done<small>.html</small></a></li><li><a href="./manual/async.html">async<small>.html</small></a></li><li><a href="./manual/camera.html">camera<small>.html</small></a></li><li><a href="./manual/click.html">click<small>.html</small></a></li><li><a href="./manual/code-a-part.html">code-a-part<small>.html</small></a></li><li><a href="./manual/combo.html">combo<small>.html</small></a></li><li><a href="./manual/config.html">config<small>.html</small></a></li><li><a href="./manual/create-element.html">create-element<small>.html</small></a></li><li><a href="./manual/dialog.html">dialog<small>.html</small></a></li><li><a href="./manual/display.html">display<small>.html</small></a></li><li><strong><a href="./manual/donkey/index.html">donkey</a></strong></li><li><a href="./manual/emoji.html">emoji<small>.html</small></a></li><li><a href="./manual/error.html">error<small>.html</small></a></li><li><strong><a href="./manual/fs/index.html">fs</a></strong></li><li><strong><a href="./manual/game/index.html">game</a></strong></li><li><a href="./manual/html-decode.html">html-decode<small>.html</small></a></li><li><a href="./manual/input.html">input<small>.html</small></a></li><li><a href="./manual/interpreter.html">interpreter<small>.html</small></a></li><li><strong><a href="./manual/issue-2228/index.html">issue-2228</a></strong></li><li><strong><a href="./manual/issue-2246/index.html">issue-2246</a></strong></li><li><strong><a href="./manual/issue-2302/index.html">issue-2302</a></strong></li><li><strong><a href="./manual/issue-2304/index.html">issue-2304</a></strong></li><li><strong><a href="./manual/issue-7015/index.html">issue-7015</a></strong></li><li><a href="./manual/multi.html">multi<small>.html</small></a></li><li><a href="./manual/multiple-editors.html">multiple-editors<small>.html</small></a></li><li><a href="./manual/no-error.html">no-error<small>.html</small></a></li><li><strong><a href="./manual/no_sab/index.html">no_sab</a></strong></li><li><strong><a href="./manual/piratical/index.html">piratical</a></strong></li><li><a href="./manual/py-editor.html">py-editor<small>.html</small></a></li><li><a href="./manual/py-editor-failure.html">py-editor-failure<small>.html</small></a></li><li><strong><a href="./manual/py-terminals/index.html">py-terminals</a></strong><ul><li><a href="./manual/py-terminals/no-repl.html">no-repl<small>.html</small></a></li><li><a href="./manual/py-terminals/repl.html">repl<small>.html</small></a></li></ul></li><li><a href="./manual/py_modules.html">py_modules<small>.html</small></a></li><li><strong><a href="./manual/service-worker/index.html">service-worker</a></strong></li><li><a href="./manual/split-config.html">split-config<small>.html</small></a></li><li><a href="./manual/submit.html">submit<small>.html</small></a></li><li><a href="./manual/target.html">target<small>.html</small></a></li><li><a href="./manual/test_display_HTML.html">test_display_HTML<small>.html</small></a></li><li><a href="./manual/test_when.html">test_when<small>.html</small></a></li><li><a href="./manual/worker.html">worker<small>.html</small></a></li></ul></li><li><strong><a href="./python/index.html">python</a></strong></li></ul></body>
 </html>
diff --git a/core/tests/python/tests/test_events.py b/core/tests/python/tests/test_events.py
index f9e37b99..ffe03e15 100644
--- a/core/tests/python/tests/test_events.py
+++ b/core/tests/python/tests/test_events.py
@@ -22,6 +22,17 @@ def teardown():
     container.innerHTML = ""
 
 
+def test_event_no_result():
+    """
+    If an event has not been triggered with a result, accessing the result
+    parameter raises a ValueError.
+    """
+    event = Event()
+    with upytest.raises(ValueError) as e:
+        event.result
+    assert str(e.exception) == "Event has not been triggered yet. No result available."
+
+
 def test_event_add_listener():
     """
     Adding a listener to an event should add it to the list of listeners. It
@@ -35,6 +46,52 @@ def test_event_add_listener():
     assert listener in event._listeners  # The item is the expected listener.
 
 
+def test_event_add_invalid_listener():
+    """
+    Adding an invalid listener should raise a ValueError.
+    """
+    event = Event()
+    with upytest.raises(ValueError) as e:
+        event.add_listener("invalid")
+    assert str(e.exception) == "Listener must be callable or awaitable."
+
+
+def test_event_add_listener_triggered():
+    """
+    Adding a listener to an event that has already been triggered should call
+    the listener immediately with the result.
+    """
+    event = Event()
+    counter = 0
+
+    def listener(x):
+        nonlocal counter
+        counter += 1
+        assert x == "ok"
+
+    event.trigger("ok")
+    event.add_listener(listener)
+    assert counter == 1  # The listener has been triggered with the expected result.
+
+
+def test_event_add_listener_multiple_times():
+    """
+    Adding the same listener multiple times should not call it multiple times.
+    """
+    event = Event()
+    counter = 0
+
+    def listener(x):
+        nonlocal counter
+        counter += 1
+        assert x == "ok"
+
+    event.add_listener(listener)
+    event.add_listener(listener)
+    event.trigger("ok")
+    assert counter == 1  # The listener has been triggered only once.
+
+
 def test_event_remove_listener():
     """
     Removing a listener from an event should remove it from the list of