Symbol.asyncIterator polyfill

define.ts

if(!Symbol.asyncIterator) {
    Object.defineProperty(Symbol, 'asyncIterator', {
        enumerable: false, // This line is optional
        configurable: false, // This line is optional
        writable: false, // This line is optional
        value: Symbol('Symbol.asyncIterator'),
    });
}

test.js

const assert = require('assert');

function equal(value, expected) {
  assert.strictEqual(value, expected);
}

function truthy(value) {
  assert.ok(value);
}

function falsy(value) {
  assert.ifError(value);
}

equal(typeof Symbol.asyncIterator, 'symbol');
/* @see https://www.ecma-international.org/ecma-262/9.0/#table-1 */
equal(Symbol.asyncIterator.toString(), 'Symbol(Symbol.asyncIterator)');
falsy(Symbol.keyFor(Symbol.asyncIterator));

const desc = Object.getOwnPropertyDescriptor(Symbol, 'asyncIterator');
truthy(desc);
/* @see https://www.ecma-international.org/ecma-262/9.0/#sec-symbol.asynciterator */
equal(desc.configurable, false);
equal(desc.enumerable, false);
equal(desc.writable, false);