How can I use decorators for validation in TypeScript?

How can I use decorators for validation in TypeScript?

You can use decorators in TypeScript to add validation logic to class properties. For example, you can create a custom decorator that checks if a value meets certain criteria before it's set.

Can you show me a simple example of a validation decorator?

Sure! Here's a basic example:

function IsString(target: any, propertyName: string) {
    let value: string;
    const getter = () => value;
    const setter = (newValue: string) => {
        if (typeof newValue !== 'string') {
            throw new Error(`${propertyName} must be a string`);
        }
        value = newValue;
    };
    Object.defineProperty(target, propertyName, { get: getter, set: setter });
}

class User {
    @IsString
    name: string;
}

This decorator checks if the name property is a string.

What if I want to validate multiple properties?

You can create multiple decorators for each property or combine validation logic within a single decorator. For example, you could create a @IsRequired decorator that checks if a property is defined.

Are there any libraries that can help with validation in TypeScript?

Yes, libraries like class-validator and yup provide powerful validation features and can work well with TypeScript.