NeatUtil.Optional

A TypeScript isomorphic adaptation of Java's Optional.

All methods of Java's Optional class are implemented except for hashCode and stream.

Installation

npm:

$ npm install neatutil.optional

yarn:

$ yarn add neatutil.optional

Basic usage

import { Optional } from 'neatutil.optional';

const emptyInstance = Optional.empty();
console.log(emptyInstance.isPresent()); // => false
console.log(emptyInstance.isEmpty()); // => true
console.log(emptyInstance.toString()); // => 'Optional.empty'

const nonEmptyInstance = Optional.of<string>('I love Espresso coffee.');
console.log(nonEmptyInstance.isPresent()); // => true
console.log(nonEmptyInstance.isEmpty()); // => false
console.log(nonEmptyInstance.get()); // => 'I love Espresso coffee.'
console.log(nonEmptyInstance.toString()); // => 'Optional[I love Espresso coffee.]'

const anotherEmptyInstance = Optional.ofNullable(null);
console.log(anotherEmptyInstance.isPresent()); // => false
console.log(anotherEmptyInstance.isEmpty()); // => true
console.log(anotherEmptyInstance.toString()); // => 'Optional.empty'

const anotherNonEmptyInstance = Optional.ofNullable<string>('I love Espresso coffee.');
console.log(anotherNonEmptyInstance.isPresent()); // => true
console.log(anotherNonEmptyInstance.isEmpty()); // => false
console.log(anotherNonEmptyInstance.get()); // => 'I love Espresso coffee.'
console.log(anotherNonEmptyInstance.toString()); // => 'Optional[I love Espresso coffee.]'

console.log(emptyInstance.equals(nonEmptyInstance)); // => false
console.log(emptyInstance.equals(anotherEmptyInstance)); // => true

console.log(nonEmptyInstance.equals(anotherNonEmptyInstance)); // => true

API

Optional<TValue>

A container object which may or may not contain a non-nullish value. If a value is present, isPresent() returns true. If no value is present, the object is considered empty and isPresent() returns false.

This is a value-based class; instances that are equal should be treated as interchangeable.

Optional is primarily intended for use as a method return type where there is a clear need to represent "no result", and where using null or undefined is likely to cause errors. A variable whose type is Optional should never itself be null or undefined; it should always point to an Optional instance.

Type Parameters:

TValue - The type of value.

static empty<TValue>(): Optional<TValue>

Returns an empty Optional instance. No value is present for this Optional.

Type Parameters:

TValue - The type of value.

Returns:

An empty Optional instance.

static of<TValue>(value: TValue): Optional<TValue>

Returns an Optional instance describing the given non-nullish value.

Type Parameters:

TValue - The type of value.

Parameters:

value - The value to describe, which must be non-nullish.

Returns:

An Optional instance with the value present.

Throws:

TypeError - If value is nullish.

static ofNullable<TValue>(value?: TValue): Optional<TValue>

Returns an Optional instance describing the given value, if non-nullish, otherwise returns an empty Optional instance.

Type Parameters:

TValue - The type of value.

Parameters:

value - The possibly-nullish value to describe.

Returns:

An Optional instance with a present value if the specified value is non-nullish, otherwise an empty Optional instance.

equals(other: Optional<TValue>): boolean

Indicates whether some other Optional instance is "equal to" this Optional instance.

The other Optional instance is considered equal if:

both instances have no value present or;
the present values are "equal to" each other.

Parameters:

other - An Optional instance to be tested for equality.

Returns:

true if the other Optional instance is "equal to" this Optional instance, otherwise false.

filter(predicate: (value: TValue) => boolean): Optional<TValue>

If a value is present, and the value matches the given predicate, returns an Optional instance describing the value, otherwise returns an empty Optional instance.

Parameters:

predicate - The predicate to apply to the value, if present.

Returns:

An Optional instance describing the value of this Optional, if a value is present and the value matches the given predicate, otherwise an empty Optional instance.

Throws:

TypeError - If predicate is not a function.

flatMap<UValue>(mapper: (value: TValue) => Optional<UValue>): Optional<UValue>

If a value is present, returns the result of applying the given Optional-bearing mapping function to the value, otherwise returns an empty Optional instance.

Type Parameters:

UValue - The type of value of the Optional instance returned by the mapping function.

Parameters:

mapper - The mapping function to apply to the value, if present.

Returns:

The result of applying an Optional-bearing mapping function to the value of this Optional, if a value is present, otherwise an empty Optional instance.

Throws:

TypeError - If mapper is not a function or does not return an Optional instance.

get(): TValue

If a value is present, returns the value, otherwise throws.

Returns:

The non-nullish value described by this Optional instance.

Throws:

Error - If no value is present.

ifPresent(action: (value: TValue) => void): void

If a value is present, performs the given action with the value, otherwise does nothing.

Parameters:

action - The action to be performed, if a value is present.

Throws:

TypeError - If action is not a function.

ifPresentOrElse(action: (value: TValue) => void, emptyAction: () => void): void

If a value is present, performs the given action with the value, otherwise performs the given empty-based action.

Parameters:

action - The action to be performed, if a value is present.

emptyAction - The empty-based action to be performed, if no value is present.

Throws:

TypeError - If action or emptyAction is not a function.

isEmpty(): boolean

If a value is not present, returns true, otherwise false.

Returns:

true if a value is not present, otherwise false.

isPresent(): boolean

If a value is present, returns true, otherwise false.

Returns:

true if a value is present, otherwise false.

map<UValue>(mapper: (value: TValue) => UValue): Optional<UValue>

If a value is present, returns an Optional instance describing the result of applying the given mapping function to the value, otherwise returns an empty Optional instance.

Type Parameters:

UValue - The type of the value returned from the mapping function.

Parameters:

mapper - The mapping function to apply to a value, if present.

Returns:

An Optional instance describing the result of applying a mapping function to the value of this Optional, if a value is present, otherwise an empty Optional instance.

Throws:

TypeError - If mapper is not a function.

or(supplier: () => Optional<TValue>): Optional<TValue>

If a value is present, returns an Optional instance describing the value, otherwise returns an Optional instance produced by the supplying function.

Parameters:

supplier - The supplying function that produces an Optional instance to be returned.

Returns:

An Optional instance describing the value of this Optional, if a value is present, otherwise an Optional instance produced by the supplying function.

Throws:

TypeError - If supplier is not a function or does not return an Optional instance.

orElse(other: TValue | null = null): TValue | null

If a value is present, returns the value, otherwise returns other.

Parameters:

other - The value to be returned, if no value is present. May be nullish.

Returns:

The value, if present, otherwise other.

orElseGet(supplier: () => TValue | null): TValue | null

If a value is present, returns the value, otherwise returns the result produced by the supplying function.

Parameters:

supplier - The supplying function that produces a value to be returned.

Returns:

The value, if present, otherwise the result produced by the supplying function.

Throws:

TypeError - If supplier is not a function.

orElseThrow(): TValue

If a value is present, returns the value, otherwise throws.

Returns:

The non-nullish value described by this Optional.

Throws:

Error - If no value is present.

orElseGetThrow<TError extends Error>(errorSupplier: () => TError): TValue

If a value is present, returns the value, otherwise throws an error produced by the error supplying function.

Type Parameters:

TError - Type of the error to be thrown.

Parameters:

errorSupplier - The supplying function that produces an error to be thrown.

Returns:

The value, if present.

Throws:

TError - If no value is present.

TypeError - If errorSupplier is not a function or does not return an Error instance.

toString(): string

Returns a non-empty string representation of this Optional suitable for debugging.

Returns:

The string representation of this instance.