I have a callback that I am using like
return innerArray.reduce((prev, curr, i, array) => {
However, when I try to use the array (for me this is an array of objects) like
array[i-1].outerIndex
I get a JavaScript error that I cannot read a property of undefined, reading outerIndex. The only way I was able to get this to work is with
let prevObj = { ...array[i - 1] };
prevObj.outerIndex
Is there something that is not an array in the argument passed to the reduce callback?
Is there something that is not an array in the argument passed to the reduce callback?
No. It is an array.
The error message says that array[i-1] is undefined.
This is probably when it is dealing with the first item in the array so i is 0 so you are trying to access array[-1] which is out of bounds.