ReflectTypeMethods.js

'use strict';

const { isProxy } = require('util').types;

const { getProxyDetails } = process.binding('util');
const hasOwnProperty = (v, n) => Reflect.apply(Object.hasOwnProperty, v, [n]);

Object.defineProperty(Symbol, 'typeOf', {
  enumerable: false,
  configurable: false,
  value: Symbol('Symbol.typeOf'),
});

const AsyncFunction = (async () => {}).constructor;
const GeneratorFunction = (function* x() {}).constructor; // eslint-disable-line no-empty-function

const labels = [
  BigInt, 'BigInt',
  Boolean, 'Boolean',
  Function, 'Function',
  Number, 'Number',
  Object, 'Object',
  String, 'String',
  Symbol, 'Symbol',

  Array, 'Array',
  Int8Array, 'Int8Array',
  Int16Array, 'Int16Array',
  Int32Array, 'Int32Array',
  Uint8Array, 'Uint8Array',
  Uint8ClampedArray, 'Uint8ClampedArray',
  Uint16Array, 'Uint16Array',
  Uint32Array, 'Uint32Array',
  BigInt64Array, 'BigInt64Array',
  BigUint64Array, 'BigUint64Array',
  Float32Array, 'Float32Array',
  Float64Array, 'Float64Array',

  ArrayBuffer, 'ArrayBuffer',
  DataView, 'DataView',
  SharedArrayBuffer, 'SharedArrayBuffer',

  AsyncFunction, 'AsyncFunction',
  GeneratorFunction, 'GeneratorFunction',

  Error, 'Error',
  EvalError, 'EvalError',
  RangeError, 'RangeError',
  ReferenceError, 'ReferenceError',
  SyntaxError, 'SyntaxError',
  TypeError, 'TypeError',
  URIError, 'URIError',

  Set, 'Set',
  Map, 'Map',
  WeakMap, 'WeakMap',
  WeakSet, 'WeakSet',

  Date, 'Date',
  Promise, 'Promise',
  RegExp, 'RegExp',

  WebAssembly.Module, 'WebAssembly Module',
  WebAssembly.Instance, 'WebAssembly Instance',
  WebAssembly.Memory, 'WebAssembly Memory',
  WebAssembly.Table, 'WebAssembly Table',
  WebAssembly.CompileError, 'WebAssembly CompileError',
  WebAssembly.LinkError, 'WebAssembly LinkError',
  WebAssembly.RuntimeError, 'WebAssembly RuntimeError',
];

const kIdentity = Symbol('[[Identity]]');
const kIdentityOnPrototype = Symbol('[[IdentityOnPrototype]]');

for (let i = 0; i < labels.length; i += 2) {
  const thisKID = Symbol(labels[i + 1]);
  Object.defineProperty(labels[i], kIdentity, {
    enumerable: false,
    configurable: false,
    writable: false,
    value: thisKID,
  });
  Object.defineProperties(labels[i].prototype, {
    [Symbol.typeOf]: {
      enumerable: false,
      configurable: false,
      writable: true,
      value: labels[i + 1],
    },
    [kIdentityOnPrototype]: {
      enumerable: false,
      configurable: false,
      writable: false,
      value: thisKID,
    },
  });
}

Reflect.typeOf = (value) => {
  if (value == null) {
    return undefined;
  }

  if (isProxy(value)) {
    const [target, handler] = getProxyDetails(value);
    if (hasOwnProperty(handler, 'typeOf')) {
      return handler.typeOf(target);
    }
    return Reflect.typeOf(target);
  }

  const type = value[Symbol.typeOf];
  if (type != null) {
    return type;
  }

  return undefined;
};

Reflect.is = (value, type) => {
  if (value == null || type == null) {
    throw new TypeError(`Cannot compare ${value} against ${type}`);
  }
  if (isProxy(value)) {
    const [target, handler] = getProxyDetails(value);
    if (hasOwnProperty(handler, 'is')) {
      return handler.is(target, type);
    }
    return Reflect.is(target, type);
  }

  const typeSymbol = type[kIdentity];
  const valueSymbol = value[kIdentityOnPrototype];
  return typeSymbol === valueSymbol;
};

Symbol.checkType.js

'use strict';

Object.defineProperty(Symbol, 'getType', {
  enumerable: false,
  configurable: false,
  value: Symbol('Symbol.getType'),
});

const AsyncFunction = (async () => {}).constructor;
const GeneratorFunction = (function* x() {}).constructor; // eslint-disable-line no-empty-function

const labels = [
  BigInt, 'BigInt',
  Boolean, 'Boolean',
  Function, 'Function',
  Number, 'Number',
  Object, 'Object',
  String, 'String',
  Symbol, 'Symbol',

  Array, 'Array',
  Int8Array, 'Int8Array',
  Int16Array, 'Int16Array',
  Int32Array, 'Int32Array',
  Uint8Array, 'Uint8Array',
  Uint8ClampedArray, 'Uint8ClampedArray',
  Uint16Array, 'Uint16Array',
  Uint32Array, 'Uint32Array',
  BigInt64Array, 'BigInt64Array',
  BigUint64Array, 'BigUint64Array',
  Float32Array, 'Float32Array',
  Float64Array, 'Float64Array',

  ArrayBuffer, 'ArrayBuffer',
  DataView, 'DataView',
  SharedArrayBuffer, 'SharedArrayBuffer',

  AsyncFunction, 'AsyncFunction',
  GeneratorFunction, 'GeneratorFunction',

  Error, 'Error',
  EvalError, 'EvalError',
  RangeError, 'RangeError',
  ReferenceError, 'ReferenceError',
  SyntaxError, 'SyntaxError',
  TypeError, 'TypeError',
  URIError, 'URIError',

  Set, 'Set',
  Map, 'Map',
  WeakMap, 'WeakMap',
  WeakSet, 'WeakSet',

  Date, 'Date',
  Promise, 'Promise',
  RegExp, 'RegExp',

  WebAssembly.Module, 'WebAssembly Module',
  WebAssembly.Instance, 'WebAssembly Instance',
  WebAssembly.Memory, 'WebAssembly Memory',
  WebAssembly.Table, 'WebAssembly Table',
  WebAssembly.CompileError, 'WebAssembly CompileError',
  WebAssembly.LinkError, 'WebAssembly LinkError',
  WebAssembly.RuntimeError, 'WebAssembly RuntimeError',
];

const kType = Symbol('[[Type]]');
for (let i = 0; i < labels.length; i += 2) {
  Object.defineProperty(labels[i], Symbol.getType, {
    enumerable: false,
    configurable: true,
    writable: true,
    value: (v) => v[kType],
  });
  Object.defineProperty(labels[i].prototype, kType, {
    enumerable: false,
    configurable: false,
    writable: false,
    value: labels[i + 1],
  });
}