Working with ReadOnly Types in TypeScript

Working with readonly Types in TypeScript

TypeScript’s readonly type modifier is a powerful tool to help manage state in object-oriented programming. It allows you to designate which data fields can be modified after creation. Unlike traditional JavaScript objects, readonly properties cannot be changed once they are set. This makes them an ideal choice for defining immutable values that need to be kept secure and consistent.

Understanding ReadOnly Types

Readonly types are defined with the readonly keyword. This code is used to indicate that the property can only be given a value once. After that, it cannot be changed. For example, if we define a Person class with readonly properties, it would look something like this:

class Person {
    readonly name: string;
    readonly age: number;
}

In this example, the name and age properties both have the readonly keyword, which means they cannot be changed once they are set.

Working with ReadOnly Types

Now that we understand what readonly types are, let’s look at how we can use them in our projects. Readonly types can be set when an instance is first created, and they cannot be changed afterwards. This means that they can be used to safely store sensitive information, such as passwords or API keys, and ensure that they remain unchanged.

For example, if we wanted to create a User class with a password property, we could make it readonly so that it is not changed after it is set:

class User {
    readonly password: string;
    // ...
}

We can then set the password property when creating a new instance:

const user = new User({
    password: 'my_secure_password'
});

Once this is done, the password property cannot be changed. This ensures that the data remains secure and consistent.

Conclusion

TypeScript’s readonly type modifier is a great way to ensure that data is kept secure and consistent. By using it, you can designate which properties can and cannot be changed after creation. This makes it an ideal choice for storing sensitive data.