Replace element at specific position in an array without mutating it

Question

How can the following operation be done without mutating the array:

let array = [\'item1\'];
console.log(array); // [\'item1\']
array[2] = \'item2\'; // array is         


        

Answer 1

The fast way

function replaceAt(array, index, value) {
  const ret = array.slice(0);
  ret[index] = value;
  return ret;
}

See the JSPerf (thanks to @Bless)

Related posts:

• Javascript fastest way to duplicate an Array - slice vs for loop
• https://github.com/lodash/lodash/issues/2053#issuecomment-188776090