sum of several arrays

1function sum_array(arr) {
2  
3  // store our final answer
4  var sum = 0;
5  
6  // loop through entire array
7  for (var i = 0; i < arr.length; i++) {
8    
9    // loop through each inner array
10    for (var j = 0; j < arr[i].length; j++) {
11      
12      // add this number to the current final sum
13      sum += arr[i][j];
14      
15    }
16    
17  }
18  
19  return sum;
20  
21}
22
23sum_array([[3, 2], [1], [4, 12]]);
24