How to 'repeat' an array n times

You could do this:

var repeated = [].concat(... new Array(100).fill([1, 2, 3]));

That creates an array of a given length (100 here) and fills it with the array to be repeated ([1, 2, 3]). That array is then spread as the argument list to [].concat().

Oh wait just

var repeated = new Array(100).fill([1, 2, 3]).flat();

would be a little shorter.

One quick way is joining the array, repeating it using string.repeat(), then splitting it and finally using ES6 Spreads

The other answer are probably better. This is just a simpel one-liner.

let arr = [1, 2, 3];
let res = [...arr.join("").repeat(3).split("").map(Number)];

console.log(res);

Use Array.from() to create an array with a length of the multiplier, where each item contains the original array. Then use Array.flat() to convert to a single array:

const multiplyArray = (arr, length) => 
  Array.from({ length }, () => arr).flat()

const arr = [1,2,3]
const arr2 = multiplyArray(arr, 3)

console.log(arr2)

You could create an array with the wanted length and map the values.

var array = [1, 2, 3],
    result = Array.from({ length: 3 * array.length }, (_, i) => array[i % array.length]);

console.log(result);