TypeScript Type Aliases and Interfaces
TypeScript allows types to be defined separately from the variables that use them.
Aliases and Interfaces allows types to be easily shared between different variables/objects.
Type Aliases
Type Aliases allow defining types with a custom name (an Alias).
Type Aliases can be used for primitives like string or more complex types such as objects and arrays:
Example
type CarYear = number
type CarType = string
type CarModel = string
type Car = {
year: CarYear,
type: CarType,
model: CarModel
}
const carYear: CarYear = 2001
const carType: CarType = "Toyota"
const carModel: CarModel = "Corolla"
const car: Car = {
year: carYear,
type: carType,
model: carModel
};
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Interfaces
Interfaces are similar to type aliases, except they only apply to object types.
Example
interface Rectangle {
height: number,
width: number
}
const rectangle: Rectangle = {
height: 20,
width: 10
};
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Extending Interfaces
Interfaces can extend each other's definition.
Extending an interface means you are creating a new interface with the same properties as the original, plus something new.
Example
interface Rectangle {
height: number,
width: number
}
interface ColoredRectangle extends Rectangle {
color: string
}
const coloredRectangle: ColoredRectangle = {
height: 20,
width: 10,
color: "red"
};
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