How to 'repeat' an array n times [duplicate]

Question

In python you can do:

arr = [1,2,3] * 3
print(arr)

output:

[1,2,3,1,2,3,1,2,3]

Is there a concise way of doing this in java script? The best I can think of is something like:

let arr2 = [...arr, ...arr, ...arr]

but if I wanted to do this 100 times it would be impractical. In python I would just multiply it by 100.

Answer 1

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.

Answer 2

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);