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Function: filter()

Call Signature​

filter<T>(option, predicate): Option<T>

Defined in: option/filter/index.ts:35

Filters an Option based on a predicate.

If the Option is Some and the predicate returns true, returns the Option unchanged. If the Option is Some and the predicate returns false, returns None. If the Option is None, returns None unchanged.

Type Parameters​

T​

T

Parameters​

option​

Option<T>

The Option to filter

predicate​

(value) => boolean

Function to test the value

Returns​

Option<T>

The filtered Option

Example​

// Data-first
filter(some(5), x => x > 0) // => Some(5)
filter(some(-5), x => x > 0) // => None
filter(none(), x => x > 0) // => None

// Data-last (in pipe)
pipe(
  fromNullable(user.age),
  filter(age => age >= 18),
  map(age => `Adult: ${age}`)
)

See​

  • map - for transforming values
  • flatMap - for chaining operations

Call Signature​

filter<T>(predicate): (option) => Option<T>

Defined in: option/filter/index.ts:36

Filters an Option based on a predicate.

If the Option is Some and the predicate returns true, returns the Option unchanged. If the Option is Some and the predicate returns false, returns None. If the Option is None, returns None unchanged.

Type Parameters​

T​

T

Parameters​

predicate​

(value) => boolean

Function to test the value

Returns​

The filtered Option

(option): Option<T>

Parameters​

option​

Option<T>

Returns​

Option<T>

Example​

// Data-first
filter(some(5), x => x > 0) // => Some(5)
filter(some(-5), x => x > 0) // => None
filter(none(), x => x > 0) // => None

// Data-last (in pipe)
pipe(
  fromNullable(user.age),
  filter(age => age >= 18),
  map(age => `Adult: ${age}`)
)

See​

  • map - for transforming values
  • flatMap - for chaining operations