1
var sumSubarrayMins = function (arr) {
2
  M = 10 ** 9 + 7;
3
  stack = [-1];
4
  res = 0;
5
  arr.push(0);
6

7
  for (let i2 = 0; i2 < arr.length; i2++) {
8
    while (arr[i2] < arr[stack[stack.length - 1]]) {
9
      i = stack.pop();
10
      i1 = stack[stack.length - 1];
11
      Left = i - i1;
12
      Right = i2 - i;
13
      res += Left * Right * arr[i];
14
    }
15
    stack.push(i2);
16
  }
17

18
  return res % M;
19
};