facebook/react · error · Error

Expected `${registrationName}` listener to be a function, in

Error message

Expected `${registrationName}` listener to be a function, instead got a value of `${typeof listener}` type.

What it means

Error "Expected `${registrationName}` listener to be a function, instead got a value of `${typeof listener}` type." thrown in facebook/react.

Source

Thrown at packages/react-dom-bindings/src/events/getListener.js:72

): Function | null {
  const stateNode = inst.stateNode;
  if (stateNode === null) {
    // Work in progress (ex: onload events in incremental mode).
    return null;
  }
  const props = getFiberCurrentPropsFromNode(stateNode);
  if (props === null) {
    // Work in progress.
    return null;
  }
  // $FlowFixMe[invalid-computed-prop]
  const listener = props[registrationName];
  if (shouldPreventMouseEvent(registrationName, inst.type, props)) {
    return null;
  }

  if (listener && typeof listener !== 'function') {
    throw new Error(
      `Expected \`${registrationName}\` listener to be a function, instead got a value of \`${typeof listener}\` type.`,
    );
  }

  return listener;
}

View on GitHub (pinned to eafeac097b)

When it happens

Trigger: Thrown at packages/react-dom-bindings/src/events/getListener.js:72 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of facebook/react@eafeac097b (2026-08-21). Data as JSON: /api/errors/6ffa6a6473112fed. Report an issue: GitHub.