The Pick Type in TypeScript: How to Create Types by Picking Properties from Other Types
TypeScript is a popular language for building scalable and maintainable applications. One of the key features of TypeScript is its ability to define and use types. In this post, we will explore the Pick type in TypeScript, which allows us to create new types by picking properties from other types.
The Pick type is a built-in utility type in TypeScript that allows us to create new types by picking properties from an existing type. It takes two type arguments: the first argument is the source type, and the second argument is a string literal or union of string literals representing the names of the properties to pick.
Here's an example of how to use the Pick type:
type Person = {
name: string;
age: number;
address: {
street: string;
city: string;
country: string;
};
};
type PersonName = Pick<Person, 'name'>;
In this example, we have defined a Person type with three properties: name, age, and address. We then create a new type called PersonName by using the Pick type and specifying the Person type as the source type and the string literal 'name' as the property to pick. The resulting type is a new type with only the name property from the Person type.
The Pick type is particularly useful when we want to create subtypes of an existing type. For example, suppose we have a User type with many properties, but we only need a subset of those properties for a particular use case. We can use the Pick type to create a new type that only includes the necessary properties.
Here's an example:
type User = {
id: number;
name: string;
email: string;
createdAt: Date;
updatedAt: Date;
};
type UserSummary = Pick<User, 'id' | 'name'>;
In this example, we define a User type with five properties, including an id, name, email, createdAt, and updatedAt. We then create a new type called UserSummary by using the Pick type and specifying the User type as the source type and a union of string literals ('id' and 'name') as the properties to pick. The resulting type is a new type that only includes the id and name properties from the User type.
It's important to note that the Pick type creates a new type that only includes the specified properties. Any other properties from the source type are not included in the new type. This can be useful when we want to create subtypes, but it can also lead to unexpected behavior if we're not careful.
The Pick type can also be used with nested properties. For example, suppose we have a Person type with an address property that contains nested properties for street, city, and country. We can use the Pick type to create a new type that only includes the street and city properties.
Here's an example:
type Person = {
name: string;
age: number;
address: {
street: string;
city: string;
country: string;
};
};
type PersonAddress = Pick<Person['address'], 'street' | 'city'>;
In this example, we create a new type called PersonAddress by using the Pick type and specifying the address property of the Person type as the source type and a union of string literals ('street' and 'city') as the properties to pick. The resulting type is a new type that only includes the street and city properties from the address property of the Person type.
When using the Pick type with nested properties, it's important to remember that the resulting type only includes the specified properties and not the entire nested object. If we need to use the entire nested object, we should use the original type instead of the picked type.
The Pick type in TypeScript is a powerful tool for creating new types by picking properties from existing types. It can be particularly useful when creating subtypes or when working with nested properties. However, it's important to use the Pick type carefully and to remember that it only includes the specified properties in the resulting type.