This is an interesting aspect of contractions.
Although he'd or I'd is only for had or would, when you use it with how, why, and where, the "did" becomes 'd.
How'd it go? How did it go
Where'd you get that? Where did you get that
Why'd you do that? Why did you do that
Oddly, for these, if we want to say "would" in a contracted way, we'd say something like "why-ud" or "where-ud you get an idea like that?"
Who seems the most flexible.
Who'd you see at the party? - Who did you see...?
Who'd have thought so! Who would have thought so!
Who'd already replied when we had to cancel? Who had already replied?