iterator-prototype.js   [plain text]

function shouldBe(actual, expected)
{
    if (actual !== expected)
        throw new Error('bad value: ' + actual);
}

var iteratorPrototype = "Cocoa"[Symbol.iterator]().__proto__.__proto__;

shouldBe(iteratorPrototype !== Object.prototype, true);
shouldBe(iteratorPrototype.__proto__, Object.prototype);
shouldBe(JSON.stringify(Object.getOwnPropertyNames(iteratorPrototype)), '[]');
shouldBe(Object.getOwnPropertySymbols(iteratorPrototype).length, 1);
shouldBe(Object.getOwnPropertySymbols(iteratorPrototype)[0], Symbol.iterator);
shouldBe(iteratorPrototype[Symbol.iterator](), iteratorPrototype);
var stringIterator = "Hello"[Symbol.iterator]();
shouldBe(iteratorPrototype[Symbol.iterator].call(stringIterator), stringIterator);

function inheritIteratorPrototype(iterator)
{
    var prototype = iterator.__proto__;
    shouldBe(prototype !== iteratorPrototype, true);
    shouldBe(Object.getOwnPropertyDescriptor(prototype, 'constructor'), undefined);
    shouldBe(prototype.__proto__, iteratorPrototype);
    shouldBe(iteratorPrototype[Symbol.iterator].name, '[Symbol.iterator]');
    shouldBe(iteratorPrototype.hasOwnProperty(Symbol.iterator), true);
}

inheritIteratorPrototype("Cappuccino"[Symbol.iterator]());
inheritIteratorPrototype(new Map()[Symbol.iterator]());
inheritIteratorPrototype(new Set()[Symbol.iterator]());
inheritIteratorPrototype(new Array()[Symbol.iterator]());
inheritIteratorPrototype((function (a, b, c) { return arguments; }(0, 1, 2))[Symbol.iterator]());
inheritIteratorPrototype((function (a, b, c) { 'use strict'; return arguments; }(0, 1, 2))[Symbol.iterator]());

function testChain(iterable)
{
    // Iterator instance
    var iterator = iterable[Symbol.iterator]();
    // %MapIteratorPrototype%
    var proto1 = Object.getPrototypeOf(iterator);
    // %IteratorPrototype%
    var proto2 = Object.getPrototypeOf(proto1);

    shouldBe(proto2.hasOwnProperty(Symbol.iterator), true);
    shouldBe(proto1.hasOwnProperty(Symbol.iterator), false);
    shouldBe(iterator.hasOwnProperty(Symbol.iterator), false);
    shouldBe(iterator[Symbol.iterator](), iterator);
}

testChain("Cocoa");
testChain(new Map());
testChain(new Set());
testChain(new Array());