question about Basic:Recursion

[qqibrow]

I was fascinated by the solution of reduce function. Can anyone tell me about your thoughts here? How you analysis this problem and tackle it step by step? Thank you!

[fkysly]

My solution:
function reduce(arr, fn, initial) {
if (!arr.length)
return;
initial = fn(inital, arr[0], 0, arr);
reduce(arr.slice(1), fn, initial);
return initial;
}
module.exports = reduce;

The simple method to solve this problem is using loop to execute the "fn" many times, then the initial will be the right answer.
Like this:

funtion reduce(arr, fn, initial) {
for(var k = 0; k < arr.length, k++) {
initial = fn(initial, arr[k], k, arr);
}
...

But we can't use loop to solve this problem.

Recursion is another method to solve this problem.We can't use recursion in the "fn", because we can't override this function, but we can use recursion in our reduce function to execute the "fn" function many times, and make the inintial be the right answer.

[ghost]

@fkysly, that's a good solution and it's what i've done at first. But the index agrument in callback function becomes useless this way, because it's always equal to 0, so user can't get the index of the item in the array.