TypeScript: use private or public in constructor

Question

I'm new to TypeScript world, and I've seen examples with this to deal with injected objects and set it to a property of the component (this.anything)

First with public and setting by hand to this.nav

export class XPTO {
   constructor(public nav: NavController) {
      this.nav = nav;
   }
}

and this, with private

export class XPTO {
   constructor(private nav: NavController) {
      //this.nav is nav?
   }
}

in both cases after construct the object this.nav is a NavController object. What are the differences of both implementations? Or this is the same when compiled to plain javascript?

Possible duplicate of Understanding "public" / "private" in typescript class — Nitzan Tomer
– Nitzan Tomer, Commented Oct 3, 2016 at 21:28
The linked duplicate doesn't do a good job of answering the question — Ryan Cavanaugh
– Ryan Cavanaugh, Commented Oct 3, 2016 at 22:43

jumping_monkey · Accepted Answer · 2023-05-24 08:34:57Z

23

Actually in your first example the explicit assignment is not needed at all:

export class XPTO {
   constructor(public nav: NavController) {
       // This line is not required when we have an access modifier (private/public) on the constructor parameter(s)
       // this.nav = nav;
       this.someFunction();
   }
   someFunction(){
       console.log(this.nav); // Prints out the NavController.
   }
}

Whenever you specify public or private on a constructor parameter a corresponding public/private variable is created on the class and filled with the value of the parameter.

So really, the only difference of the two code samples is that one is private and the other one is public.

The resulting JavaScript will be the same. However, the compiler will throw an error, if you are trying to access private variables in your code.

edited May 24, 2023 at 8:34

jumping_monkey

8,1152 gold badges60 silver badges75 bronze badges

answered Oct 3, 2016 at 21:30

Pape

3011 silver badge9 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Kewin Dousse · Accepted Answer · 2016-10-03 21:27:20Z

3

public and private, as a lot of Typescript features, are only TypeScript modifiers. I'm not sure the compiler names these variables exactly the same, but from a JavaScript point of view, the code will be essentially the same.

The interest of Typescript is to give you features like type checking, it doesn't necessarily always modifies the outputted code.

answered Oct 3, 2016 at 21:27

Kewin Dousse

4,0592 gold badges29 silver badges50 bronze badges

Collectives™ on Stack Overflow

TypeScript: use private or public in constructor

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related