libnyanpasu/clash-nyanpasu · warning

Proxy addEventListener:

Error message

Proxy addEventListener:

What it means

The bootstrap script in index.html wraps a global object's addEventListener to intercept 'change' listeners. If addEventListener is called with fewer than 2 arguments or with an event name other than 'change', it logs console.error('Cannot proxy addEventListener:', arguments) and refuses to register the listener. If called with more than 2 arguments but event 'change', it logs console.warn('Proxy addEventListener:', arguments) and registers via addListener.

Source

Thrown at frontend/nyanpasu/index.html:25

      href="./assets/image/logo.ico"
      type="image/x-icon"
    />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title><%- title %></title>
    <%- injectScript %>
    <script>
      ;(function () {
        var _matchMedia = window.matchMedia
        window.matchMedia = function () {
          var v = _matchMedia.apply(null, arguments)
          if (!v.addEventListener) {
            v.addEventListener = function () {
              if (arguments.length < 2 || arguments[0] !== 'change') {
                console.error('Cannot proxy addEventListener:', arguments)
                return
              }
              if (arguments.length > 2) {
                console.warn('Proxy addEventListener:', arguments)
              }
              v.addListener(arguments[1])
            }
          }
          return v
        }
      })()
    </script>
  </head>
  <body>
    <div id="root"></div>
    <script type="module" src="/src/main.tsx"></script>
  </body>
</html>

View on GitHub (pinned to f7dbce2997)

Solutions

  1. Check the logged `arguments` to see which event name and how many arguments were passed.
  2. If the code registers a non-'change' event on this object, that's unsupported — rework the script to attach other events to the proper target (document/window) instead of this proxied object.
  3. If it's a legitimate 'change' listener with a third options argument, use addListener(handler) directly or pass only (event, handler) to silence the warn.
  4. If you control the wrapper and new event support is needed, extend the proxy to forward additional event types instead of erroring.

Example fix

// before (third argument triggers the proxy warning)
v.addEventListener('change', handler, { passive: true });
// after
v.addEventListener('change', handler);
// or
v.addListener(handler);
Defensive patterns

Strategy: fallback

Validate before calling

if (typeof v.addEventListener === 'function' && arguments.length >= 2 && arguments[0] === 'change') {
  v.addEventListener('change', arguments[1]);
} else {
  v.addListener(arguments[1]);
}

Type guard

function supportsAddEventListener(v: unknown): v is { addEventListener(type: 'change', fn: () => void): void } {
  return typeof v === 'object' && v !== null &&
    typeof (v as any).addEventListener === 'function';
}

Prevention

When it happens

Trigger: Any script (or webview-injected code) calling that proxied object's addEventListener with an event type other than 'change' (or with missing handler argument) — e.g. document/element-style code doing el.addEventListener('click', fn) on the proxied global, or a library adding a change listener with extra options (capture/useCapture third argument).

Common situations: A vendored library or user script assumes standard DOM addEventListener semantics (any event name, optional options object) but the proxied object only supports a single 'change' event; upgrade of a dependency introduces new addEventListener calls for other events.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of libnyanpasu/clash-nyanpasu@f7dbce2997 (2026-09-08). Data as JSON: /api/errors/cb41ed1483d5c402. Report an issue: GitHub.