Why an access modifier on an argument in a constructor?

Question

typescript

I came across this construction in the tutorials:
constructor(private heroService: HeroService) { }
At first I decided that the "private" access modifier in that place was a mistake, but I found that the tutorial would not compile without it.
I must have missed something when reading the typescript docs.
Tell me what it is, poke it into the docks, or at least tell me what it's called to drive it into Google?

Answer 1

this is the shorthand syntax for declaring a field: www.typescriptlang.org/docs/handbook/classes.html , section Parameter properties.