Equal side array, linear solution

function makePSA(arr) {
    const PSA = new Array(arr.length + 1);
    let sum = 0;

    for (let i = 0; i <= arr.length; i++) {
        PSA[i] = sum;
        sum += arr[i];
    }

    return PSA;
}

function queryPSA(PSA, start, end) {
    return (PSA[end] - PSA[start]) || 0;
}

function findEvenIndex(arr) {
    const PSA = makePSA(arr);

    for (let index = 0; index <= arr.length; index++) {
        let leftSum = queryPSA(PSA, 0, index);
        let rightSum = queryPSA(PSA, index + 1, arr.length);

        console.log(index, leftSum, rightSum);

        if (leftSum === rightSum) {
            return index;
        }
    }

    return -1;
}