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Function: unary()

unary<A, R>(fn): (a) => R

Defined in: function/arity/index.ts:37

Creates a function that only accepts one argument, ignoring additional arguments.

This is useful when passing functions to higher-order functions that provide multiple arguments, but you only want to use the first one.

Type Parameters​

A​

A

R​

R

Parameters​

fn​

(a, ...rest) => R

Returns​

(a): R

Parameters​

a​

A

Returns​

R

Examples​

// parseInt takes two arguments, which causes issues with map
['1', '2', '3'].map(parseInt)           // => [1, NaN, NaN] (unexpected!)
['1', '2', '3'].map(unary(parseInt))    // => [1, 2, 3] (correct)
const logFirst = unary(console.log)

['a', 'b', 'c'].forEach(logFirst)
// Logs:
// a
// b
// c
// (without indices or array)
// Wrapping functions for cleaner callbacks
const parseNumber = unary(Number)
const inputs = ['42', '3.14', '100']

inputs.map(parseNumber)  // => [42, 3.14, 100]