Assigning Typescript constructor parameters

Question

I have interface:

export interface IFieldValue {
    name: string;
    value: string;
}

And I have a class that implements it:

class Person implements IFieldValue{
    name: string;
    value: string;
    constructor (name: string, value: string) {
        this.name = name;
        this.value = value;
    }
}

after reading this post I've thinking about refactoring:

class Person implements IFieldValue{
    constructor(public name: string, public value: string) {
    }
}

Question : In first class I have fields which by default should be as private. In second sample I can only set them as public. Is it all correct in my understanding of default Access modifiers in TypeScript?

Mauricio Gracia Gutierrez · Accepted Answer · 2021-02-14 18:43:25Z

34

Public by default. TypeScript Documentation

In following definition

class Person implements IFieldValue{
    name: string;
    value: string;
    constructor (name: string, value: string) {
        this.name = name;
        this.value = value;
    }
}

Attributes <Person>.name and <Person>.value are public by default.

as they are here

class Person implements IFieldValue{
    constructor(public name: string, public value: string) {
        this.name = name;
        this.value = value;
    }
}

Beware: Here is an incorrect way of doing it, since this.name and this.value will be regarded as not defined in the constructor.

class Person implements IFieldValue{
    constructor(name: string, value: string) {
        this.name = name;
        this.value = value;
    }
}

To make these attributes private you need to rewrite it as

class Person implements IFieldValue{
    private name: string;
    private value: string;
    constructor (name: string, value: string) {
        this.name = name;
        this.value = value;
    }
}

or equivalently

class Person implements IFieldValue{
    constructor (private name: string, private value: string) {}
}

For TypeScript 2.X since the interace has the properties as public, you need to change the private to public and also export the classes

export class Person implements IFieldValue{
    constructor (public name: string, public value: string) {}
}

which in my opinion is the most preferable way that avoids redundancy.

edited Feb 14, 2021 at 18:43

Mauricio Gracia Gutierrez

11k7 gold badges81 silver badges115 bronze badges

answered Jan 29, 2017 at 16:30

Maciej Caputa

1,91114 silver badges23 bronze badges

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

4 Comments

phil_lgr Over a year ago

If Person implements IFieldValue which has public properties 'name' and 'value' then name and value must remain public in the Person class. The two code examples you provided do not compile with TypeScript 2.x. You either change the interface and make props private or you could have private props personName and personValue like:

class Person implements IFieldValue{     private personName: string;     private personValue: string;     constructor (public name: string, public value: string) {         this.personName = name;         this.personValue = value;     } }

phil_lgr Over a year ago

sorry disregard the part where I said: "You either change the interface and make props private" makes no sense since props are only public on an interface

ruffin Over a year ago

fwiw, I guessed wrong when dealing with an injected parameter I wanted to declare private. Still works like above, but the @Inject comes before the private. @Inject(MyType) private _myType: MyType,

Mauricio Gracia Gutierrez Over a year ago

@phil_lgr I have updated the answer with important clarifications for TypeScript 2.X

Collectives™ on Stack Overflow

Assigning Typescript constructor parameters

1 Answer 1

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related