ReactiveX/rxjs · error · TypeError

${String(key)} must be callable

Error message

${String(key)} must be callable

What it means

Error "${String(key)} must be callable" thrown in ReactiveX/rxjs.

Source

Thrown at packages/observable-polyfill/src/index.ts:341

  }

  const integer = Math.trunc(number);
  const range = 2 ** 64;
  if (integer > 0 && integer < range) {
    return integer;
  }

  const remainder = integer % range;
  return remainder < 0 ? remainder + range : remainder;
}

function getMethod(value: object, key: PropertyKey): Callable | undefined {
  const method = (value as Record<PropertyKey, unknown>)[key];
  if (method == null) {
    return undefined;
  }
  if (typeof method !== 'function') {
    throw new TypeError(`${String(key)} must be callable`);
  }
  return method as Callable;
}

function getSyncIteratorRecord<T>(value: object): SyncIteratorRecord<T> {
  const iteratorMethod = getMethod(value, Symbol.iterator);
  if (!iteratorMethod) {
    throw new TypeError('Object does not define a callable Symbol.iterator method');
  }

  const iterator = iteratorMethod.call(value);
  if (!isObject(iterator)) {
    throw new TypeError('Symbol.iterator must return an object');
  }

  const next = getMethod(iterator, 'next');
  if (!next) {
    throw new TypeError('Iterator must define a callable next() method');

View on GitHub (pinned to 54796b38a5)

When it happens

Trigger: Thrown at packages/observable-polyfill/src/index.ts:341 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of ReactiveX/rxjs@54796b38a5 (2026-08-28). Data as JSON: /api/errors/e073b046dad666f0. Report an issue: GitHub.