Union and Intersection Types
Union and intersection types in TypeScript allow you to write more flexible and expressive type definitions. A union type uses the pipe symbol (|) to indicate that a value can be one of several types.
An intersection type uses the ampersand (&) to combine multiple types into one. The resulting type must satisfy all the properties of each type involved.
1234567891011121314// Union type: a value can be a string OR a number let userId: string | number; userId = "abc123"; userId = 42; // Intersection type: a value must have properties of both types type Name = { name: string }; type Age = { age: number }; type Person = Name & Age; const person: Person = { name: "Alice", age: 30, };
In the code above, userId can be either a string or a number, so you can assign both "abc123" and 42 to it. This is helpful when a variable might accept more than one type, such as an ID that could be stored as a string or a number.
In the code sample, the Person type is an intersection of the Name and Age types, so an object of type Person must have both a name property of type string and an age property of type number. This is useful when you want to combine several type definitions into a single, more specific one.
Choosing between union and intersection types depends on your needs: use a union when a value can be one of several types, and use an intersection when a value must satisfy all the types at once.
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When should I use a union type versus an intersection type?
Are there any common pitfalls when using these types in TypeScript?
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Union and intersection types in TypeScript allow you to write more flexible and expressive type definitions. A union type uses the pipe symbol (|) to indicate that a value can be one of several types.
An intersection type uses the ampersand (&) to combine multiple types into one. The resulting type must satisfy all the properties of each type involved.
1234567891011121314// Union type: a value can be a string OR a number let userId: string | number; userId = "abc123"; userId = 42; // Intersection type: a value must have properties of both types type Name = { name: string }; type Age = { age: number }; type Person = Name & Age; const person: Person = { name: "Alice", age: 30, };
In the code above, userId can be either a string or a number, so you can assign both "abc123" and 42 to it. This is helpful when a variable might accept more than one type, such as an ID that could be stored as a string or a number.
In the code sample, the Person type is an intersection of the Name and Age types, so an object of type Person must have both a name property of type string and an age property of type number. This is useful when you want to combine several type definitions into a single, more specific one.
Choosing between union and intersection types depends on your needs: use a union when a value can be one of several types, and use an intersection when a value must satisfy all the types at once.
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