Class Optional<T>

A special type that encourages the move away from null and undefined.

An Optional is immutable and is a wrapper type of T | null | undefined that provides useful functions for transformation and safe retrieval of an optional value.

Type Parameters

T
type of the value within this optional.

Index

Properties

Accessors

get hasValue isEmpty

Methods

equals exists flatMap getOrElse map orElse isDefined isOptional of

Properties

`Private` optValue

optValue: OptionalValue<T>

Accessors

get

get get(): OptionalValue<T>
Get the value contained within the optional. The value is returned without any checks, so it might be null or undefined.

Returns OptionalValue<T>

hasValue

get hasValue(): boolean
Returns true if this optional is not empty, false otherwise.

Returns boolean

isEmpty

get isEmpty(): boolean
Returns true if this optional is empty, false otherwise

Returns boolean

Methods

equals

equals(other): boolean
Utility for checking equality against the value contained within this optional
Parameters
- other: T
  value to check against
Returns boolean
true if this optional is this value

exists

exists(predicate): boolean
If there's a value, returns the result of applying a predicate on the value contained within this optional, or false when no value exists.
Parameters
- predicate: ((value) => boolean)
  function that test the value
  - - (value): boolean
    - Parameters
      value: T
      Returns boolean
Returns boolean
false if this optional is empty or the result of applying the predicate

flatMap

flatMap<U>(transformer): Optional<U>
Same as map, but the transformation must return an optional. Does nothing if this optional is empty.
Type Parameters
- U
Parameters
- transformer: ((value) => Optional<U>)
  a transformation function
  - - (value): Optional<U>
    - Parameters
      value: T
      Returns Optional<U>
Returns Optional<U>
an optional with the transformation potentially applied

getOrElse

getOrElse(defaultValue): T
Returns the value contained within this optional if it exists or returns a default value supplied.
Parameters
- defaultValue: T
  value returned if this optional is empty
Returns T
the value contained or default supplied.

map

map<U>(transformer): Optional<U>
Apply a transformation on the value contained within this optional. Does nothing if this optional is empty.
Type Parameters
- U
Parameters
- transformer: ((value) => U)
  a transformation function
  - - (value): U
    - Parameters
      value: T
      Returns U
Returns Optional<U>
an optional with the transformation potentially applied

orElse

orElse(alternative): Optional<T>
Returns this optional if it has a value or an alternative provided optional
Parameters
- alternative: Optional<T>
Returns Optional<T>
this or alternative

`Static` isDefined

isDefined<U>(opt): opt is U
Checks that a value is neither null nor undefined.

Has the added benefit of type narrowing in typescript.
Type Parameters
- U
Parameters
- opt: OptionalValue<U>
  value that can be undefined or null
Returns opt is U
true if the value is neither undefined or null

`Static` isOptional

isOptional(value): value is Optional<unknown>
Parameters
- value: unknown
  checks if a value is an Optional
Returns value is Optional<unknown>

`Static` of

of<U>(value): Optional<NonOptionalType<U>>
The preffered way to create an optional. This also automatically unwraps optionals if you try to create an optional of an optional.
Type Parameters
- U
Parameters
- value: OptionalValue<U>
  to be treated as an optional
Returns Optional<NonOptionalType<U>>
a new Optional

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