Uncaught TypeError: Cannot read property 'push' of undefined. What should be done?

Question

I get the following error

"Uncaught TypeError: Cannot read property 'push' of undefined"

When I try to run the following code:

function chunkArrayInGroups(arr, size) {
  // Break it up.

   var arr_final=[];
   for(var i=0,j=0;i<arr.length;i++)
   {
    arr_final[j].push(arr[i]);
    if(i===size)
    {
        j++;
    }
   }
   return arr_final;
}

console.log(chunkArrayInGroups(["a", "b", "c", "d"], 2));

Can anyone help?

Answer 1

Instead of

arr_final[j].push(arr[i]);

do something like

arr_final.push(arr[i]);

Answer 2

You forgot to initialize each chunk with an empty array. Corrected code below:

function chunkArrayInGroups(arr, size) {
  // Break it up.

  var arr_final=[[]]; // <-- initialize chunk
  for(var i=0,j=0;i<arr.length;i++)
  {
    arr_final[j].push(arr[i]);
    if(i===size)
    {
      arr_final.push([]); // <-- initialize chunk
      j++;
    }
  }
  return arr_final;
}

console.log(chunkArrayInGroups(["a", "b", "c", "d"], 2));

I'm guessing there is also an error in your chunking logic, so probably what you really want is:

function chunkArrayInGroups(arr, size) {
  // Break it up.

  var arr_final=[];
  for(var i=0,j=-1;i<arr.length;i++)
  {
    if (i % size === 0) {
      arr_final.push([]);
      j++;
    }
    arr_final[j].push(arr[i]);
  }
  return arr_final;
}

console.log(chunkArrayInGroups(["a", "b", "c", "d"], 2));

Answer 3

In order to split your input array into multiple chunks with length ≤ size, you need to initialize a new empty chunk arr_final.push([]) each time your iterator variable i has reached a multiple of size - which you can check via the modulo operator:

 function chunkArrayInGroups(arr, size) { // Break it up. var arr_final = []; for (var i = 0, j = -1; i < arr.length; ++i) { if (i % size == 0) { arr_final.push([]); j++; } arr_final[j].push(arr[i]); } return arr_final; } console.log(chunkArrayInGroups(["a", "b", "c", "d", "e"], 3));