Cannot read property 'length' of undefined. Function assumes arr[i] is undefined

Asked Aug 30 '21 at 08:50

Active Aug 30 '21 at 08:50

Viewed 18 times

This function keeps returning error "Cannot read property 'length' of undefined" at line 4.

Why is arr[i] undefined?

function filteredArray(arr, elem) {
    let newArr = []
    for (i = 0; i <= arr.length; i++) {
        for (j = 0; j <= arr[i].length; j++) {
            if (arr[i][j] != elem) {
                newArr.push(i)
            }
        }

    }
    return newArr
}

let result = (filteredArray([
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9, 0]
], 3))

console.log(result)

asked Aug 30 '21 at 08:50

John Bartmann

4

`i <= arr.length` -> `i < arr.length`. When `i === arr.length` it's out of bounds of the array, since the indexes are `0` to `length-1`. – VLAZ Aug 30 '21 at 08:51
This also means that `j <= arr[i].length` should be `j < arr[i].length` – VLAZ Aug 30 '21 at 08:53
Thank you, very helpful. Low on sleep today. – John Bartmann Aug 30 '21 at 09:03

Cannot read property 'length' of undefined. Function assumes arr[i] is undefined

0 Answers0