Function createSequenceConverter

lib/internal/webidl.js:773–824

* Creates a converter for a Web IDL sequence type. * @see https://webidl.spec.whatwg.org/#es-sequence * @param {Converter} converter Element converter. * @returns {Converter}

(converter)

 * @returns {Converter}
 */
function createSequenceConverter(converter) {
  return function(V, options = kEmptyObject) {
    // Web IDL sequence conversion step 1: require an ECMA-262 Object.
    if (type(V) !== 'Object') {
      throw makeException(
        'cannot be converted to sequence.',
        options);
    }

    // Step 2: GetMethod(V, %Symbol.iterator%).
    const method = V[SymbolIterator];
    // Step 3: throw if the iterator method is undefined, null, or not callable.
    if (typeof method !== 'function') {
      throw makeException(
        'cannot be converted to sequence.',
        options);
    }

    // Step 4 and create-sequence step 1: get the iterator record.
    const iterator = FunctionPrototypeCall(method, V);
    const nextMethod = iterator?.next;
    if (typeof nextMethod !== 'function') {
      throw makeException(
        'cannot be converted to sequence.',
        options);
    }

    // Create-sequence step 2: initialize i to 0.
    const idlSequence = [];
    while (true) {
      // Step 3.1: IteratorStepValue(iteratorRecord).
      const next = FunctionPrototypeCall(nextMethod, iterator);
      if (type(next) !== 'Object') {
        throw makeException(
          'cannot be converted to sequence.',
          options);
      }
      // Step 3.2: IteratorComplete applies ToBoolean(done).
      if (next.done) {
        break;
      }
      // Step 3.3: convert next to an IDL value of type T.
      const idlValue = converter(
        next.value,
        makeOptions(options, sequenceElementContext(idlSequence.length, options)),
      );
      // Step 3.4: store the value and advance i.
      ArrayPrototypePush(idlSequence, idlValue);
    }
    return idlSequence;
  };
}

/**
 * Creates a converter for a Web IDL interface type.