TypeScript Readonly <Type> Utility Type
In this article, we are going to learn about Readonly<Type> Utility Type in Typescript. Typescript is a popular programming language used for building scalable and robust applications. One of the features of Typescript is Readonly<Type> Utility Type which is used to create a new type where all properties are readonly, meaning they cannot be modified once assigned a value.
Syntax
interface GFG {
name: string;
age: number;
}
const g: Readonly<GFG> = {
name: 'John',
age: 30
};
Example 1: In this example, we will see how to make a variable Readonly.
Javascript
/* Define an interface Person with three properties: name, age, and address */ interface Person { name: string; age: number; } /* Declare a Readonly constant called person with the Person type and assign it a value of { name: 'John', age: 30 } */ const person: Readonly<Person> = { name: 'John' , age: 30 }; /* Log the person constant to the console to see the output */ console.log(person); |
Output:
Example 2: In this example, we will try to change the readonly property of our object. We will get an error.
Javascript
/* Define an interface Person with three properties: name, age, and address */ interface Person { name: string; age: number; } /* Declare a Readonly constant called person with the Person type and assign it a value of { name: 'John', age: 30 } */ const person: Readonly<Person> = { name: 'John' , age: 30 }; /* Log the person constant to the console to see the output */ person.name= 'Akshit' ; console.log(person); |
Output:
Reference: https://www.typescriptlang.org/docs/handbook/utility-types.html#readonlytype
Contact Us