missing values - fill empty array slots

Linda

Hi Community I struggle to understand the following behavior. Its a typicall Monday problem. All I want is to fill the empty array slots with the integer 0.

myArray = [
  [1, ,1, ],
  [ , ,1, ],
  [ , ,1, ],
  [1, , , ],
]
      
for (var a = 0; a < myArray.length; a++) {
  for (var b = 0; b < myArray[a].length; b++) {
    if (myArray[a][b] == undefined) {
        myArray[a][b] = 0
    }
  }
  console.log("myArray[" + a + "]["+ b +"]" + " = " + myArray[a][b])
}