after checking for parameter presence, consistently use one of "set" or "let"

[michaelficarra]

Like

If _proto_ is not present, set _proto_ to %Array.prototype%.

or

If _hostDefined_ is not present, let _hostDefined_ be ~empty~.

I think we mostly say "set" in these cases, but there are some occurrences that use "let". I prefer "set" since I consider even optional parameters to already declare the alias.

[jmdyck]

I see only two occurrences of the "let" form: the one given, and one in ToPrimitive.

[ljharb]

It would be really nice to have a nicer syntax for defaulting absent AO arguments than an imperative assignment :-)

[michaelficarra]

Eh, kind of. Every bit of sugar we add means the readers need to learn that sugar. The way it is right now is nice and explicit, for example with regard to ordering, without needing to learn anything new.

[ljharb]

There's a defaulting syntax the readers should already know, though - =