Interfaces allow you to construct the shape of certain implementation. Interfaces should not really be a new concept to you considering your background in .NET, and in TypeScript it is very much the same.
Interfaces are defined using the keyword interface, as follows:
enum Operand {
Sum, Subtract, Multiply, Divide
}
interface Calculable {
left: number;
right: number;
operand: Operand;
}Furthermore, interfaces support optional members and read-only properties, too:
interface Calculable {
readonly left: number;
readonly right: number;
operand?: Operand;
}In the preceding example, the Calculable interface has two readonly properties, left and right, as well as an optional operand property. Read-only declarations can only be set when first initialized or inside the constructor of the owning class.
Like other interface-supporting languages, you can code a certain hierarchy of interfaces by extending them.