Javascript Gotcha — forEach loop

When using forEach to iterate through an array of int and define a variable “total”, and then expect to sum up every element in the array in some ways to “total”. For example, the following code is doing exactly what I described above.

function minimumWaitingTime(queries) {
queries = queries.sort((a, b) => a - b);
  let total
  queries.forEach((query, index) => {
    total += query * (queries.length - (index + 1));
  });
  return total;
}
const array = [3, 2, 1, 2, 6];
minimumWaitingTime(array);

however, it does not work and total inside each loop is logged as NaN. The solution to make it work is to initialize “total” as 0.

function minimumWaitingTime(queries) {
queries = queries.sort((a, b) => a - b);
let total = 0
queries.forEach((query, index) => {
total += query * (queries.length - (index + 1));
});
return total;
}
const array = [3, 2, 1, 2, 6];
minimumWaitingTime(array);

Now, it works as expected.