JS reduce

1. Returns single value.
2. Doesn't mutate original array.
3. Doesn't execute the function for empty array elements.
4. Syntax: array.reduce(function(previousValue, currentValue, currentIndex, arr), initialValue);

previousValue: value resulting from the previous call to callBackFn. On first call, initialValue if specified otherwise array[0].

currentValue: value of the current element.On the first call, the value of array[0] if initialValue specified otherwise array[1].

currentIndex: currentValue index. On first call it is 0 if initialValue specified otherwise 1.

Examples

---

---

---

Functional Composition:

In above, example input is function returned by (...functions) as we are calling multiply6(6). Hence input is 6.

Reference: MDN official

Thank you. :)