Sebastian Zartner sebastianzartner at
Wed Mar 5 04:04:37 PST 2014

>   But it seems the thread fizzled out a couple years ago, and
> Array.prototype.contains didn't seem to make its way into ES6. That seems
> odd, since we do have String.prototype.contains, and it seemed like it was
> desirable for DOM.
> The DOM won't inherit from it directly, shall it?

Why not? A use case would be to check whether a specific node is within a

>  It's also a standard utility function in several libraries.
>  Was it left out on purpose? If so, what was the justification?
> I predict code like this without it:
> ''[1, 2, 3], 2);  // true
> .indexOf === -1 works today for this use case and will continue to.
> I'd be happy to see !~arr.indexOf(el) disappear in favor of a use of
> .contains() though.

While .indexOf() just gets you the index of one item, .contains() could
even be extended to allow to check whether an array contains several items.

.contains([1, 2, 3], [1, 3]) // true
.contains([1, 2, 3], [1, 4]) // false

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