Better Validations with includes and Selector Function in TypeScript

As a developer, ensuring that your code is robust and free from errors is crucial. One way to achieve this is through proper validation of data inputs. TypeScript provides many tools for type checking and validation, and in this article, we will explore how to use the includes method and selector function for better validations.

The includes Method

The includes method is a built-in JavaScript method that checks if an array or string includes a specific value. In TypeScript, we can use includes to validate data inputs against a set of allowed values.

For example, let’s say we have a function that takes in a string parameter and needs to validate that it is either “foo” or “bar”. We can use includes to achieve this:

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function validateInput(input: string): boolean {
  const allowedValues = ["foo", "bar"];
  return allowedValues.includes(input);
}

In this example, we have an array allowedValues that contains the allowed values. We then use includes to check if the input parameter is included in the array. The function returns true if the input is valid and false if it is not.

The Selector Function

The selector function is a TypeScript feature that allows us to define a function that selects a specific property from an object. This can be useful when validating complex data structures.

Let’s say we have an interface Person that represents a person’s information:

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interface Person {
  name: string;
  age: number;
  email: string;
}

Now let’s say we have an array of Person objects and we want to validate that all of the email properties are valid email addresses. We can use a selector function to achieve this:

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function validateEmails(people: Person[]): boolean {
  function getEmail(person: Person): string {
    return person.email;
  }

  const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
  return people.every((person) => emailRegex.test(getEmail(person)));
}

In this example, we have a getEmail function that takes in a Person object and returns the email property. We then use every to check that every Person object in the array has a valid email address.

Cheers! 🍺