Error : undefined

[NKos]

Tell us what’s happening:
Describe your issue in detail here.

I am getting an error that says “Cannot set properties of undefined”, although I cannot see what is undefined here.
Your code so far

function chunkArrayInGroups(arr, size) {
let myArr = [];
let counter = arr.length / size;
let base = 0;
for(let i = 0; i < counter; ++i){
  let subArray = 0;
  for(let a = 0; a < size; ++a) {
myArr[i][subArray] = arr[base];
++subArray;
  }
  base = base + size;
   }
   console.log(myArr);
return myArr;
}

chunkArrayInGroups([0, 1, 2, 3, 4, 5], 3);

  **Your browser information:**

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.110 Safari/537.36

Challenge: Chunky Monkey

Link to the challenge:

freeCodeCamp.org

[JeremyLT]

When in doubt, add more console.log()s:

function chunkArrayInGroups(arr, size) {
  let myArr = [];
  let counter = arr.length / size;
  let base = 0;
  for (let i = 0; i < counter; i++) {
    let subArray = 0;
    console.log("iteration : " + i);
    console.log("  subArray : ", subArray);
    for (let a = 0; a < size; a++) {
      console.log("  inner iteration : " + a);
      console.log("    myArr : ", myArr);
      myArr[i][subArray] = arr[base];
      subArray++;
    }
    base = base + size;
  }
  console.log(myArr);
  return myArr;
}

chunkArrayInGroups([0, 1, 2, 3, 4, 5], 3);

[NKos]

I am sorry but I still couldn’t figure it out even after adding the console.logs. The undefined warning makes me think that I am trying to manipulate an element of an array that’s not defined but am I not supposed to declare an empty array? Why would it be defined anyways?

function chunkArrayInGroups(arr, size) {
  let myArr = [];
  let counter = arr.length / size;
  let base = 0;
  for(let i = 0; i < counter; ++i){
    let subArray = 0;
    
    for(let a = 0; a < size; ++a) {
      
myArr[i][subArray] = arr[base];
++subArray;
++base;

    }

     }
     console.log(myArr);
  return myArr;
}

chunkArrayInGroups([0, 1, 2, 3, 4, 5], 3);

[JeremyLT]

When I run this:

function chunkArrayInGroups(arr, size) {
  let myArr = [];
  let counter = arr.length / size;
  let base = 0;
  for (let i = 0; i < counter; i++) {
    let subArray = 0;
    console.log("iteration : " + i);
    console.log("  subArray : ", subArray);
    for (let a = 0; a < size; a++) {
      console.log("  inner iteration : " + a);
      console.log("    myArr : ", myArr);
      myArr[i][subArray] = arr[base];
      subArray++;
    }
    base = base + size;
  }
  console.log(myArr);
  return myArr;
}

chunkArrayInGroups([0, 1, 2, 3, 4, 5], 3);

I get:

iteration : 0
  subArray :  0
  inner iteration : 0
    myArr :  []
TypeError: myArr[i] is undefined

So, myArr[i] is not defined. But, if myArr[i] is not defined, then it is impossible for myArr[i][anything] to exist. You can’t assign something to a property/index of a thing that doesn’t exist.

[NKos]

Actually, I have tried removing the [subArray] and I don’t see that warning anymore, so it is probably about that part.

[NKos]

So I can’t add values to an empty array without using .push?

[JeremyLT]

You can add values to an empty array. But that’s not what you are doing. You are trying to add values to a subarray of an empty array.

// This is ok
const myArray = [];
myArray[2] = 5;
console.log(myArray);

// This is bad
const mySecondArray = [];
mySecondArray[0][2] = 5;
console.log(mySecondArray);

[NKos]

Okay, I see what I was doing wrong and I was able to pass the challenge using .push(), but I am curious if there is a way to create subarrays of an empty array without using .push function.

[JeremyLT]

Sure, you just need to define mySecondArray[0] before trying to use it:

// This is ok
const myArray = [];
myArray[2] = 5;
console.log(myArray);

// This is ok but wierd
const mySecondArray = [];
mySecondArray[0] = [];
mySecondArray[0][2] = 5;
console.log(mySecondArray);

// This is bad
const myThirdArray = [];
myThirdArray[0][2] = 5;
console.log(myThirdArray);