Interface

An interface fulfills the principle of "duck typing"

interface inputObjectI = {
	label: string
	optionalVal: string?
	readonly readOnlyVal: number // value is immutable post-declaration
}

Once we define the interface, it can then be used as a type.

Function interfaces can also be created

• ex. we have a fn with 2 params of type String and String, and the function returns Boolean

interface search {
	(source: string, substring: string): boolean
}

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Different perspectives of Interface

The purpose of an interface changes depending on if we are looking at it from an Object-Oriented perspective or a Function perspective.

Interfaces in Object-Oriented Programming

In OOP context, an interface defines a list of methods that a class needs to implement in order to conform to the interface.

• often used to fulfill the Dependency Inversion Principle from SOLID design principles.
• The dependency inversion principles says that it’s much better to have interfaces than concrete classes as dependencies.

In general, the OOP part of interfaces is their ability to express some required behavior, as opposed to data in the functional paradigm.

Interfaces in Functional Programming

In functional programming context, interfaces are used not to enumerate methods of an object, but to describe the shape of the data contained by the object.

• In this context, generic interfaces are used to describe a data shape when you don’t know or care about the exact type of some properties of the interface. It often makes sense when the data types contain some value.