Slice and Splice problem doubt

Tell us what’s happening:
Why is this code not acceptable though it prints the outputs correctly as desired?

Your code so far

function frankenSplice(arr1, arr2, n) {
  var arr = [];
  for(var i = 0;i<n;i++)
  return arr;

frankenSplice([1, 2, 3], [4, 5], 1);

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.169 Safari/537.36.

Link to the challenge:

The challenge requires you to return a 1-dimensional array. You are returning a multi-dimensional array.