Sum of several arrays

You will be given an array of several arrays that each contain integers and your goal is to write a function that will sum up all the numbers in all the arrays. For example, if the input is [[3, 2], [1], [4, 12]] then your program should output 22 because 3 + 2 + 1 + 4 + 12 = 22. Solve without and with reduce.

We will solve this challenge by looping through the entire array, and then looping through each inner array adding up all the numbers.

function sum_array(arr) {
  // store our final answer
  var sum = 0;
  // loop through entire array
  for (var i = 0; i < arr.length; i++) {
    // loop through each inner array
    for (var j = 0; j < arr[i].length; j++) {
      // add this number to the current final sum
      sum += arr[i][j];
    }
  }
  
  return sum;
}

sum_array([[3, 2], [1], [4, 12]]);

With reduce:

function sumArray(arr) {
  return arr.reduce((t, e) => t.concat(e)).reduce((t, e) => t + e)
}