30-seconds-of-code/snippets/js/s/juxtapose-functions.md

title, type, language, tags, cover, dateModified

title	type	language	tags	cover	dateModified
Juxtapose functions	snippet	javascript	function	dark-leaves-3	2020-10-20T23:29:39+03:00

Takes several functions as argument and returns a function that is the juxtaposition of those functions.

• Use Array.prototype.map() to return a fn that can take a variable number of args.
• When fn is called, return an array containing the result of applying each fn to the args.

const juxt = (...fns) => (...args) => [...fns].map(fn => [...args].map(fn));

juxt(
  x => x + 1,
  x => x - 1,
  x => x * 10
)(1, 2, 3); // [[2, 3, 4], [0, 1, 2], [10, 20, 30]]
juxt(
  s => s.length,
  s => s.split(' ').join('-')
)('30 seconds of code'); // [[18], ['30-seconds-of-code']]