How to set default property value in typescript

Question

Is it possible to have the name set by its default value with this code?

interface ProjectInterface {
  id: string;
  name?: string;
}

class Project implements ProjectInterface {
  id: string;
  name?: string = 'default name';
}

const project: Project = {id: 'hello'};

console.log(project.name);

https://playcode.io/892621

You didn't create new Project().

Jax-p
– Jax-p

2022-05-02 14:48:59 +00:00
Commented May 2, 2022 at 14:48 — Jax-p
– Jax-p, Commented May 2, 2022 at 14:48

Juulloo · Accepted Answer · 2022-05-02 14:56:16Z

2

Once you instantiate a new Project the name will take it's default value. For instantiation to work you first need to definitively assign the id in a constructor or with a default value:

class Project implements ProjectInterface {
    id: string;
    name?: string = 'default name';
 
    constructor(id: string) {
        this.id = id;
    }
}

const project: Project = new Project('hello');

answered May 2, 2022 at 14:56

Juulloo

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Comments

Anubhav Gupta · Accepted Answer · 2022-05-02 14:56:21Z

0

I don't think so. I think you can't provide default values for interfaces or type aliases as they are compile time only and default values need runtime support.

answered May 2, 2022 at 14:56

Anubhav Gupta

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