_asyncOptionalChain.ts

// https://github.com/alangpierce/sucrase/tree/265887868966917f3b924ce38dfad01fbab1329f
//
// The MIT License (MIT)
//
// Copyright (c) 2012-2018 various contributors (see AUTHORS)
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// SOFTWARE.

import type { GenericFunction } from './types';

/**
 * Polyfill for the optional chain operator, `?.`, given previous conversion of the expression into an array of values,
 * descriptors, and functions, for situations in which at least one part of the expression is async.
 *
 * Adapted from Sucrase (https://github.com/alangpierce/sucrase) See
 * https://github.com/alangpierce/sucrase/blob/265887868966917f3b924ce38dfad01fbab1329f/src/transformers/OptionalChainingNullishTransformer.ts#L15
 *
 * @param ops Array result of expression conversion
 * @returns The value of the expression
 */
export async function _asyncOptionalChain(ops: unknown[]): Promise<unknown> {
  let lastAccessLHS: unknown = undefined;
  let value = ops[0];
  let i = 1;
  while (i < ops.length) {
    const op = ops[i] as string;
    const fn = ops[i + 1] as (intermediateValue: unknown) => Promise<unknown>;
    i += 2;
    // by checking for loose equality to `null`, we catch both `null` and `undefined`
    if ((op === 'optionalAccess' || op === 'optionalCall') && value == null) {
      // really we're meaning to return `undefined` as an actual value here, but it saves bytes not to write it
      return;
    }
    if (op === 'access' || op === 'optionalAccess') {
      lastAccessLHS = value;
      value = await fn(value);
    } else if (op === 'call' || op === 'optionalCall') {
      value = await fn((...args: unknown[]) => (value as GenericFunction).call(lastAccessLHS, ...args));
      lastAccessLHS = undefined;
    }
  }
  return value;
}

// Sucrase version:
// async function _asyncOptionalChain(ops) {
//   let lastAccessLHS = undefined;
//   let value = ops[0];
//   let i = 1;
//   while (i < ops.length) {
//     const op = ops[i];
//     const fn = ops[i + 1];
//     i += 2;
//     if ((op === 'optionalAccess' || op === 'optionalCall') && value == null) {
//       return undefined;
//     }
//     if (op === 'access' || op === 'optionalAccess') {
//       lastAccessLHS = value;
//       value = await fn(value);
//     } else if (op === 'call' || op === 'optionalCall') {
//       value = await fn((...args) => value.call(lastAccessLHS, ...args));
//       lastAccessLHS = undefined;
//     }
//   }
//   return value;
// }