[removed] Make an array of value pairs form an array of values

Question

Is there an elegant, functional way to turn this array:

[ 1, 5, 9, 21 ]

into this

[ [1, 5], [5, 9], [9, 21] ]

I kn

Answer 1

You may do as follows with just a sinle liner of .reduce() with no initial;

var arr = [ 1, 5, 9, 21 ],
  pairs = arr.reduce((p,c,i) => i == 1 ? [[p,c]] : p.concat([[p[p.length-1][1],c]]));
console.log(pairs);