microsoft/playwright · error · DOMException

Failed to execute 'close' on 'WebSocket': The close code mus

Error message

Failed to execute 'close' on 'WebSocket': The close code must be either 1000, or between 3000 and 4999. ${code} is neither.

What it means

Error "Failed to execute 'close' on 'WebSocket': The close code must be either 1000, or between 3000 and 4999. ${code} is neither." thrown in microsoft/playwright.

Source

Thrown at packages/injected/src/webSocketMock.ts:229

        this.addEventListener('message', this._onmessageListener as any);
    }

    send(message: WebSocketMessage): void {
      if (this.readyState === WebSocketMock.CONNECTING)
        throw new DOMException(`Failed to execute 'send' on 'WebSocket': Still in CONNECTING state.`);
      if (this.readyState !== WebSocketMock.OPEN)
        throw new DOMException(`WebSocket is already in CLOSING or CLOSED state.`);
      if (this._passthrough) {
        if (this._ws)
          this._apiSendToServer(message);
      } else {
        messageToData(message, data => binding({ type: 'onMessageFromPage', id: this._id, data }));
      }
    }

    close(code?: number, reason?: string): void {
      if (code !== undefined && code !== 1000 && (code < 3000 || code > 4999))
        throw new DOMException(`Failed to execute 'close' on 'WebSocket': The close code must be either 1000, or between 3000 and 4999. ${code} is neither.`);
      if (this.readyState === WebSocketMock.OPEN || this.readyState === WebSocketMock.CONNECTING)
        this.readyState = WebSocketMock.CLOSING;
      if (this._passthrough)
        this._apiCloseServer(code, reason, true);
      else
        binding({ type: 'onClosePage', id: this._id, code, reason, wasClean: true });
    }

    // --- methods called from the routing API ---

    _apiEnsureOpened() {
      // This is called at the end of the route handler. If we did not connect to the server,
      // assume that websocket will be fully mocked. In this case, pretend that server
      // connection is established right away.
      if (!this._ws)
        this._ensureOpened();
    }

View on GitHub (pinned to c8fc3bf8d3)

When it happens

Trigger: Thrown at packages/injected/src/webSocketMock.ts:229 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of microsoft/playwright@c8fc3bf8d3 (2026-08-12). Data as JSON: /api/errors/4e2bab7db48326f2. Report an issue: GitHub.