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| // ECMA used the name Symbol.iterator. Symbols offer names that are unique and cannot clash | |
| // with other property names. Also, Symbol.iterator will return an object called an iterator. | |
| // This iterator will have a method called next which will return an object with keys value and done. | |
| const iterable = { | |
| [Symbol.iterator]() { | |
| let step = 0; | |
| const iterator = { | |
| next() { | |
| step++; | |
| if (step === 1) { | |
| return { value: 'This', done: false } | |
| } else if (step === 2) { | |
| return { value: 'is', done: false } | |
| } else if (step === 3) { | |
| return { value: 'iterable', done: true } | |
| } | |
| return { value: undefined, done: false }; | |
| } | |
| } | |
| return iterator | |
| } | |
| } | |
| // var iterator = iterable[Symbol.iterator](); | |
| // console.log(iterator.next()); | |
| // console.log(iterator.next()); | |
| // console.log(iterator.next()); | |
| // console.log(iterator.next()); | |
| // console.log(iterator.next()); | |
| const myFavouriteAuthors = { | |
| allAuthors: { | |
| fiction: [ | |
| 'Agatha Christie', | |
| 'J. K. Rowling', | |
| 'Dr. Seuss' | |
| ], | |
| scienceFiction: [ | |
| 'Neal Stephenson', | |
| 'Arthur Clarke', | |
| 'Isaac Asimov', | |
| 'Robert Heinlein' | |
| ], | |
| fantasy: [ | |
| 'J. R. R. Tolkien', | |
| 'J. K. Rowling', | |
| 'Terry Pratchett' | |
| ], | |
| }, | |
| [Symbol.iterator]() { | |
| const genres = Object.values(this.allAuthors); | |
| // console.log('genres', genres); | |
| let currentAuthorIndex = 0; | |
| let currentGenreIndex = 0; | |
| return { | |
| next() { | |
| const authors = genres[currentGenreIndex]; | |
| const doNothaveMoreAuthors = !(currentAuthorIndex < authors.length); | |
| if (doNothaveMoreAuthors) { | |
| currentGenreIndex++; | |
| currentAuthorIndex = 0; | |
| } | |
| const doNotHaveMoreGenres = !(currentGenreIndex < genres.length); | |
| if (doNotHaveMoreGenres) { | |
| return { | |
| value: undefined, | |
| done: true | |
| }; | |
| } | |
| return { | |
| value: genres[currentGenreIndex][currentAuthorIndex++], | |
| done: false | |
| } | |
| } | |
| }; | |
| } | |
| }; | |
| for (const author of myFavouriteAuthors) { | |
| console.log(author); | |
| } | |
| console.log(...myFavouriteAuthors) |
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