Is “.then(function(a){ return a; })” a no-op for promises?

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It seems to me like .then(function (a) { return a; }) is just a no-op. Right?

Yes.1

It is useless and should be omitted.

What’s going on and why did the author write it that way?

It’s a blunder. Or the author didn’t understand promises.

1: If they aren’t the same, what’s the difference?

As always, there are some edge cases. Really weird ones. That no-one should use (without extensive commenting):
a) it returns a new promise instance, a distinct object, to avoid sharing. However, .then() would as well.
b) a is tested again for its thenable-ness. If it suddenly became a promise since the fulfillment, it now will be awaited. This would be awful of course.

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