Yes, the ES6 `length` function would return 0 for [undefined, 2, 3]. I hope it was only used as an example in the article and nobody is planning to really use t

Yes, the ES6 `length` function would return 0 for [undefined, 2, 3]. I hope it was only used as an example in the article and nobody is planning to really use this. (Edit: see sibling comment; the article is already aware of this issue.) And yes, ES6 pattern matching is still quite limited.