What to use for data-only objects in TypeScript: Class or Interface?

Use classes with parameter properties:

// Immutable data object
class Person {
  constructor(readonly firstName: String, readonly lastName: String) {}
}

// Mutable data object
class Person {
  constructor(public firstName: String, public lastName: String) {}
}

To store data-only objects you should use POJO, and in Typescript describe structures using interfaces/types

If you want to store data, use an object or an array.

If you want data with attached logic, use a class.

Storing data without attached logic in a class is a misuse of features of your programming language

From https://github.com/reduxjs/redux/issues/4649#issuecomment-1872426846

Note that classes are not specific to TypeScript, they are a JavaScript feature.

I use classes for my data in Typescript, as I allways did in C# C++ Java, and only use interfaces for dependency injection. Interfaces have not be thought for manipulating data.

In my application model, if I need to write a method that uses some datas of the same class, then the class is better place to go for that method. Adding getters and setters that transform your properties is a great flexibility.

I am not a javascript programmer so when I need to create an object, I don't like using data only object where properties can by anything. I create an instance of class by the way of the constructors that have been defined for that class.

When I receive data from a service, I don't deserialize a class: I deserialize the json data and I create my instance with that data. Here is the way for building my model from the received data:

// ajax callback for diaries
onReceiveDiary( jsonDiary : any )
{
   let newDiary = new Diary ( jsonDiary );

   // now I can call methods on the object:
   let ok : boolean = newDiary.CheckIfCompleted();
}

In the class I add a constructor with the only one dependency on the json object:

export class Diary
{
   title : string;
   article : Article;

   constructor( json : any )
   {
      // the trick for setting all the object properties
      $.extend( this, json);

      this.article = new Article( json.article );
   }
}

Or we can create a factory for building objects using the default constructor:

   let newDiary = new Diary ();
   $.extend( newDiary, jsonDiary );
   newDiary.article = $.extend( new Article(), jsonDiary.article );