JSFiddle - React, Tailwind, and code Playground

JavaScript

function insert(target, source, position) {
  Array.prototype.splice.apply(target, [position,0].concat(source));
}

var numbers = [1,3,5,7,9,11];
var letters = ['a','b','c'];

var anotherRef = numbers

insert(numbers, letters, 1)

console.log(anotherRef)