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Automatic Assignment of Constructor Parameters in TypeScript

Automatic Assignment of Constructor Parameters in TypeScript

What is Parameter Property TypeScript?

The TypeScript has so many useful features which not have in other programming languages. The TypeScript has an automatic assignment of constructor parameters that is called “Parameter Property”.

It is automatic assignment of constructor parameters to the relevant property. It is great but it is different to other languages.


Examples as,

Declaring a class with constructor arguments in C# and other programming language as,

class Customer {
    _name: string;
    _age: number;
    _adrress: string;

    constructor(name: string, age: number, adrress: string) {
        this.name = _name;
        this.age = _age;
        this.adrress = _adrress;
    }
}

Declaring a class with constructor arguments in TypeScript –that is called automatic parameter assignment as,

export class Customer {
    constructor(private name: string, age: number, private adrress: string) { }
}

You can take a look at this on the JavaScript.

var Customer = (function () {
    function Customer(name, age, adrress) {
        this.name = name;
        this.age = age;
        this.adrress = adrress;
    }

    return Customer;
})();

Public, Private, and Protected modifiers as
1.     Public - accessible outside of the class
2.     Private - only accessible in the class only
3.     Protected - accessible in the class and the derived classes

Public modifier by default - When you are not put a modifier (public, private or protected) on your member definition then TypeScript will choose the public by default.

Which access modifiers are implied when not specified?
Everything in a class is public if not specified. Everything in a module is private unless export keyword is used.

What is the purpose of the public access modifier for classes in Typescript?
Your sample code means exactly the same in TypeScript. When you don't put a modifier public, private or protected on your member definition then TypeScript will choose the default one which is public.


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