Type Assertion, also known as Type Casting, is a feature in TypeScript that allows you to explicitly define the type of a value when the type system cannot infer it automatically. It provides a way to override the default type inference and treat a value as a specific type.

Example

Imagine you're working with an external library that doesn't have TypeScript support or has incomplete type definitions. In such cases, the type inference may not accurately capture the types of the library's API responses or objects. This lack of type safety can lead to potential bugs or limitations in your code.

Type Assertion enables you to assert the correct type for such scenarios. Let's say you have an API response that returns data in a generic response variable. By using type assertion, you can explicitly define the type of the response variable, ensuring proper type checking and enabling IDE auto-completion:

const response = getApiResponse(); // Assume response is of type any

const parsedData = response as ApiResponse;

In this example, the as keyword is used for type assertion, where ApiResponse is the desired type. This allows you to work with parsedData confidently, leveraging TypeScript's type checking and auto-completion.

Conclusion

Type Assertion empowers developers to handle scenarios where type inference falls short, providing flexibility and control over types in TypeScript. It enables seamless integration with external libraries and allows for safer and more reliable coding practices.