Juxtapose functions

JavaScript, Function · Oct 20, 2020

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']]

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