TypeScript and field initializers

Question

How to init a new class in TS in such a way (example in C# to show what I want):

// ... some code before
return new MyClass { Field         


        

Answer 1

I wanted a solution that would have the following:

• All the data objects are required and must be filled by the constructor.
• No need to provide defaults.
• Can use functions inside the class.

Here is the way that I do it:

export class Person {
  id!: number;
  firstName!: string;
  lastName!: string;

  getFullName() {
    return `${this.firstName} ${this.lastName}`;
  }

  constructor(data: OnlyData) {
    Object.assign(this, data);
  }
}

const person = new Person({ id: 5, firstName: "John", lastName: "Doe" });
person.getFullName();

All the properties in the constructor are mandatory and may not be omitted without a compiler error.

It is dependant on the OnlyData that filters out getFullName() out of the required properties and it is defined like so:

// based on : https://medium.com/dailyjs/typescript-create-a-condition-based-subset-types-9d902cea5b8c
type FilterFlags = { [Key in keyof Base]: Base[Key] extends Condition ? never : Key };
type AllowedNames = FilterFlags[keyof Base];
type SubType = Pick>;
type OnlyData = SubType any>;

Current limitations of this way:

• Requires TypeScript 2.8
• Classes with getters/setters