concatenate array to array with specific positions JavaScript

October 6, 2022

i have a array of array like below.

  const array1 = [[8,1,2,3,1],[3,1,1,1],[4,2,1]];

what i need to do is append six empty values " " in-between last two values for each element.

Expected output:

[ [ 8, 1, 2, '', '', '', '', '', '', 3, 1 ],
  [ 3, 1 '', '', '', '', '', '' , 1, 1,],
  [ 4, '', '', '', '', '', '', 2, 1 ] ]

What i tried:

i know how to append this to end of each element like below. can I modify my code with adding positioning?
What is the most efficient way to do this?

 const array1 = [[8,1,2,3,1],[3,1,1,1],[4,2,1]];
const appendArray = new Array(6).fill('');
const map1 = array1.map(x => x.concat(appendArray));
console.log(map1)

>Solution :

Array .splice could be one way

const array1 = [[8,1,2,3,1],[3,1,1,1],[4,2,1]];
const map1 = array1.map(x => {
  const copy = [...x];
  copy.splice(-2, 0, ...Array(6).fill(''))
  return copy;
})
console.log(map1)

Although … personally I hate splice … this is better because it’s a one liner :p

const array1 = [[8,1,2,3,1],[3,1,1,1],[4,2,1]];
const map1 = array1.map(x => [...x.slice(0, -2), ...Array(6).fill(''), ...x.slice(-2)])
console.log(map1)