Optional.ts

Optional.ts emulate Optional class of Java lang.

Instllation

To install Optinal.ts, use npm.

$ npm i @xiangma9712/optional.ts

Then import to your project.

import Optional from "@xiangma9712/optional.ts";

Dependency

TypeScript: >=2.8.1

Method Summery

Modifier and Type	Method	Description
static Optional<T>	empty<T>()	Returns an empty Optional.
Optional<T>	filter(predicate: (T)=> boolean)	If value is present, and the value matches the given predicate, return an Optional describing the value, otherwise return an empty Optional.
Optional<U>	flatmap(mapper: (T) => Optional<U>)	If a value is present, apply the provided Optional-bearing mapping function to it, return that result, otherwise return an empty Optional.
T	get()	If a value is present, returns the value, otherwise throws 'No Such Element'
any	ifPresent(consumer: (T) => any)	If a value is present, invoke the specified consumer with the value, otherwise do nothing.
boolean	isPresent()	Return true if there is a value present, otherwise false.
Optional<U>	map(mapper: (T) => U)	If a value is present, apply the provided mapping function to it, and if the result is non-null, return an Optional describing the result.
Optinal<T>	of(value: NonNullable)	Returns an Optional with the specified present non-null value.
Optinal<T>	ofNullable(value: T)	Returns an Optional describing the specified value, if non-null, otherwise returns an empty Optional.
T	ofElse(other: T)	Return the value if present, otherwise return other.
T	orElseGet(supplier: (...any) => T)	Return the value if present, otherwise invoke supplier and return the result of that invocation.
T	orElseThrow(message: string)	Return the contained value, if present, otherwise throw an error with the message

Note

• of(null) doesn't throw an error
  Unlike Java Optional, Optional.of(null) doesn't throw an error. Since the argument of of() is defined as NonNullable<T>, you will see the following error message in coding.

Argument of type 'null' is not assignable to parameter of type 'never'. ts(2345)

• ifPresnt() can return value
  In Optional.ts, you can use function which returns value as a argument of ifPresent() method.