Simple reduce function

reduce.js

// array to reduce
// combine is a function that will do something to the current value and the current element
// current is either the start provided or 0 if nothing is provided?

function reduce(array, combine, start) {
  var current = start || 0;
  for (var i = 0; i < array.length; i++)
    current = combine(current, array[i]);
  return current;
}

console.log(reduce([1, 2, 3, 4], function(a, b) {
  return a + b;
}, 0));
// → 10

From Eloquent JS