Javascript Multiplying Within an Array

I have an array with multiple arrays inside. I would like to multiply the contents of each array.

Here is my code–currently not getting anything in console.
The desired output is 3 numbers– the result of multiplication of the three arrays

var arr = [
  [1, 2, 3],
  [3, 4],
  [7, 8, 9]
]
var mult = 1
for (i = 0; i < arr.length; i++) {
  for (j = 0; j < arr.length; j++) {
    mult *= arr[i][j]
  }
  console.log(mult)
}