Resize multidirectional arrays JavaScript Google script

I need to resize arrays by adding empty new columns and empty new rows.

Ex

newRows = 2

newCols = 3

(1s are just placeholder for any data)
arr= [ 
     [1,1,1,1],
     [1,1,1,1],
     [1,1,1,1],
    ];

To

arr= [ 
      [1,1,1,1,"","",""],
      [1,1,1,1,"","",""],
      [1,1,1,1,"","",""],
      ["","","","","","",""],
      ["","","","","","",""],
     ];

I can get the new empty cols but not the new empty rows

function resizeArr() {

let  arr= [ 
      [1,1,1,1],
      [1,1,1,1],
      [1,1,1,1],
     ];

let newCols =3 
    newRows = 2;
  
  //Add new empty cols
  arr.forEach((row) => {
    row[arr.length+newCols]="";
  });

  console.log(arr)
}

How to add new empty rows ?

Thanks

>Solution :

let arr = [
  [1,1,1,1],
  [1,1,1,1],
  [1,1,1,1],
];

let newCols = 3, newRows = 2

arr.forEach(i=>i.push(...Array(newCols).fill('')))
for(let i=0; i<newRows; i++) arr.push(Array(arr[0].length).fill(''))

console.log(arr)