Filter with recursion.js

const filter = ([head, ...rest] = [], callback) => {
  if(!head) return [];

  return [

   ...callback(head) ? [head] : [],
   
   ...filter(rest, callback)

   ];
};


console.log(filter([], () => true).length === 0);
console.log(filter([1, 2, 3], (val) => val === 1).length === 1);
console.log(filter([1, 2, 3], (val) => val > 1).length === 2);
console.log(filter([1, 2, 3], (val) => val > 1));