Untitled

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>

<script id="jsbin-javascript">
function prefixSum(A) {
    var l = A.length,
        P = new Array(l),
        sum = A[0];

    P[0] = sum;

    for (let i=1; i < l; ++i ) {
      sum += A[i];
      P[i] = sum;
    }
    return P;
}

A=[1,2,3,4,5];
console.log(prefixSum(A));
</script>


<script id="jsbin-source-javascript" type="text/javascript">function prefixSum(A) {
    var l = A.length,
        P = new Array(l),
        sum = A[0];

    P[0] = sum;

    for (let i=1; i < l; ++i ) {
      sum += A[i];
      P[i] = sum;
    }
    return P;
}

A=[1,2,3,4,5];
console.log(prefixSum(A));

</script></body>
</html>