readonly

Class, type veya interfacelerde bir özelliği sadece okunabilir yapmak için readonly kullanabiliriz.

class Employee {
    readonly empCode: number;
    empName: string;
    
    constructor(code: number, name: string)     {
        this.empCode = code;
        this.empName = name;
    }
}
let emp = new Employee(10, "John");
emp.empCode = 20; //Compiler Error
emp.empName = 'Bill'; 

interface IEmployee {
    readonly empCode: number;
    empName: string;
}

let empObj:IEmployee = {
    empCode:1,
    empName:"Steve"
}

empObj.empCode = 100; // Compiler Error: Cannot change readonly 'empCode'

Readonly<> kullanarak bir obje içerisindeki tüm elemanları readonly olarak tanımlayabiliriz.

interface IEmployee {
    empCode: number;
    empName: string;
}

let emp1: Readonly<IEmployee> = {
    empCode:1,
    empName:"Steve"
}

emp1.empCode = 100; // Compiler Error: Cannot change readonly 'empCode'
emp1.empName = 'Bill'; // Compiler Error: Cannot change readonly 'empName'

let emp2: IEmployee = {
    empCode:1,
    empName:"Steve"
}

emp2.empCode = 100; // OK
emp2.empName = 'Bill'; // OK