utils.js

"use strict";

// Returns "Type(value) is Object" in ES terminology.
function isObject(value) {
  return typeof value === "object" && value !== null || typeof value === "function";
}

function hasOwn(obj, prop) {
  return Object.prototype.hasOwnProperty.call(obj, prop);
}

const getOwnPropertyDescriptors = typeof Object.getOwnPropertyDescriptors === "function" ?
  Object.getOwnPropertyDescriptors :
  // Polyfill exists until we require Node.js v8.x
  // https://tc39.github.io/ecma262/#sec-object.getownpropertydescriptors
  obj => {
    if (obj === undefined || obj === null) {
      throw new TypeError("Cannot convert undefined or null to object");
    }
    obj = Object(obj);
    const ownKeys = Reflect.ownKeys(obj);
    const descriptors = {};
    for (const key of ownKeys) {
      const descriptor = Reflect.getOwnPropertyDescriptor(obj, key);
      if (descriptor !== undefined) {
        Reflect.defineProperty(descriptors, key, {
          value: descriptor,
          writable: true,
          enumerable: true,
          configurable: true
        });
      }
    }
    return descriptors;
  };

const wrapperSymbol = Symbol("wrapper");
const implSymbol = Symbol("impl");
const sameObjectCaches = Symbol("SameObject caches");

function getSameObject(wrapper, prop, creator) {
  if (!wrapper[sameObjectCaches]) {
    wrapper[sameObjectCaches] = Object.create(null);
  }

  if (prop in wrapper[sameObjectCaches]) {
    return wrapper[sameObjectCaches][prop];
  }

  wrapper[sameObjectCaches][prop] = creator();
  return wrapper[sameObjectCaches][prop];
}

function wrapperForImpl(impl) {
  return impl ? impl[wrapperSymbol] : null;
}

function implForWrapper(wrapper) {
  return wrapper ? wrapper[implSymbol] : null;
}

function tryWrapperForImpl(impl) {
  const wrapper = wrapperForImpl(impl);
  return wrapper ? wrapper : impl;
}

function tryImplForWrapper(wrapper) {
  const impl = implForWrapper(wrapper);
  return impl ? impl : wrapper;
}

const iterInternalSymbol = Symbol("internal");
const IteratorPrototype = Object.getPrototypeOf(Object.getPrototypeOf([][Symbol.iterator]()));

function isArrayIndexPropName(P) {
  if (typeof P !== "string") {
    return false;
  }
  const i = P >>> 0;
  if (i === Math.pow(2, 32) - 1) {
    return false;
  }
  const s = `${i}`;
  if (P !== s) {
    return false;
  }
  return true;
}

const supportsPropertyIndex = Symbol("supports property index");
const supportedPropertyIndices = Symbol("supported property indices");
const supportsPropertyName = Symbol("supports property name");
const supportedPropertyNames = Symbol("supported property names");
const indexedGet = Symbol("indexed property get");
const indexedSetNew = Symbol("indexed property set new");
const indexedSetExisting = Symbol("indexed property set existing");
const namedGet = Symbol("named property get");
const namedSetNew = Symbol("named property set new");
const namedSetExisting = Symbol("named property set existing");
const namedDelete = Symbol("named property delete");

module.exports = exports = {
  isObject,
  hasOwn,
  getOwnPropertyDescriptors,
  wrapperSymbol,
  implSymbol,
  getSameObject,
  wrapperForImpl,
  implForWrapper,
  tryWrapperForImpl,
  tryImplForWrapper,
  iterInternalSymbol,
  IteratorPrototype,
  isArrayIndexPropName,
  supportsPropertyIndex,
  supportedPropertyIndices,
  supportsPropertyName,
  supportedPropertyNames,
  indexedGet,
  indexedSetNew,
  indexedSetExisting,
  namedGet,
  namedSetNew,
  namedSetExisting,
  namedDelete
};