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.