TypeScript optional in class constructor

Question

Currently learning TypeScript. I have a class:

class ComicBookCharacter {
  protected secretIdentity?: string;
  alias: string;
  health: number;
  strength: number;


  constructor({ alias, health, strength, secretIdentity }) {
    this.alias = alias;
    this.health = health;
    this.strength = strength;
    this.secretIdentity = secretIdentity;
  }
}

class SuperHero extends ComicBookCharacter {
  getIdentity() {
    console.log(`${this.alias} secret name is ${this.secretIdentity}`)
  }
}

const superman = new ComicBookCharacter({
  alias: 'Superman',
  health: 300,
  strength: 60,
  secretIdentity: undefined,
});

I'm wondering if I have to pass undefined when creating an instance of a class if I made one of the properties optional (like the secretIdentity here);

Removing secretIdentity: undefined gets me a compiler error.

Edit:

After the solution that Shift 'N Tab gave below, I did some more research and you can also specify the constructor like this:

constructor(fields: Partial<ComicBookCharacter> & {
  mothersName?: string,
  secretIdentity?: string,
}) {
  Object.assign(this, fields);
}

And as Shift 'N Tab wrote in the comment below, do not forget to add "strictPropertyInitialization": true in tsconfig file

Shift 'n Tab · Accepted Answer · 2018-06-17 02:13:45Z

2

If you wanna make an object argument in the constructor you can do that by Object destructuring approach.

class ComicBookCharacter{
    secretIdentity?: string;
    alias: string = '';
    health: number = 0;
    strength: number = 0;

    constructor(character: { alias: string, health : number, strength : number, secretIdentity?: string }) {
        Object.assign(this, character);
    }

}

edited Jun 17, 2018 at 2:13

answered Jun 16, 2018 at 1:54

Shift 'n Tab

9,51414 gold badges80 silver badges125 bronze badges

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

6 Comments

mdmb Over a year ago

But is there a way to do it when still passing an object to the constructor? I find it more clear when it comes to code readability.

mdmb Over a year ago

Thanks a lot! That’s really helpful!

mdmb Over a year ago

Just wanted to say once again that this is a really clean way to do this. One thing that pops up in my editor is that it complains the following: Property alias has no initializer and is not definitely assigned in the constructor. The same is with health and strenth

mdmb Over a year ago

I also found that it can be done with character: Partial<ComicBookCharacter>, but then you have to specify those optional fields using & { secretIdentity?: string }. I added the edit to my original post so it can maybe help some people :)

Shift 'n Tab Over a year ago

a work around to your linting error is to make "strictPropertyInitialization": true, from your tsconfig or do it safe by assigning manually each property in the constructor class or make a default property value in each declaration.

|

Paul · Accepted Answer · 2018-06-16 00:09:04Z

0

I think you can set secret identity to an empty string in the constructor ( secretIdentity = ‘’ ).

answered Jun 16, 2018 at 0:09

Paul

4782 silver badges8 bronze badges

Collectives™ on Stack Overflow

TypeScript optional in class constructor

2 Answers 2

6 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

6 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related