JSFiddle - React, Tailwind, and code Playground

by booktu8

JavaScript

var a = [1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5, 5],
  b = [11, 22, 33, 44, 55];

var s =a.reduce((acc, ele, idx) => ((idx + 1) % 3 ? acc.push(ele) : acc.push(ele, b.shift()), acc), []);


console.log(s)