Polyfill for Array.prototype.copyWithin.
$ npm install --save-dev array-copywithinFunctionally:
var copyWithin = require('array-copywithin');
var array = copyWithin([1, 2, 3, 4, 5], 0, 3);
console.log(array);
// => [4, 5, 3, 4, 5]From Array object:
require('array-copywithin/shim');
var array = [1, 2, 3, 4, 5].copyWithin(0, 3);
console.log(array);
// => [4, 5, 3, 4, 5]