I am trying to count the length of subarray at index 0. I implemented this logic written below but i got error TypeErrror: Cannot read property ‘length’ of undefined.

I know that solution does exist of this challenge but i want to do it myself. Thats why asking for help.

My code so far

```
function largestOfFour(arr) {
var i;
var realarr=[];
var sublength=[];
realarr=arr;
for(i=0;i<5;i++) {
sublength=realarr[i].length;
}
return sublength;
}
largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);
```

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.

**Link to the challenge:**

https://www.freecodecamp.org/challenges/return-largest-numbers-in-arrays