Question

I am trying to understand how the number variable is determined based on example from the book Eloquent Javascript.

When I output number I can see it growing as the loop progresses, but i can’t see where the number variable is actually set.

(Note: For anybody who understands Eloquent Javascript I have changed over the show() function to alert())

function forEach(array, action) {
  for (var i = 0; i < array.length; i++)
    action(array[i]);
}

function sum(numbers) {
  var total = 0;
  forEach(numbers, function (number) {
    total += number;
  });
  return total;
}
alert(sum([1, 10, 100, 1000]));

Answer 1

forEach(numbers, function (number) {
    total += number;
  });

In this part number is taken from the current numbers, and is equivalent to:

for (var i = 0; i < numbers.length; i++) {
  var number = numbers[i];

  function (number) {
    total += number;
  }
}