Great Work James Sinclair

Loved your Topic, even i am interested in .reduce()

The first Example will be hard for the starters to understand, So here's my Version!

.reduce()

• Accepts a callback function and an optional second parameter
• Iterates through an array
• Runs a callback on each value in the array
• The first parameter to the callback is either the first value in the array or the optional second parameter
• The first parameter to the callback is often called "accumulator"
• The returned value from the callback becomes the new value of accumulator _ Whatever is returned from the callback function, becomes the new value of the accumulator!

1. Example without adding the second parameter

var arr = [1,2,3,4,5];

arr.reduce(function(accumulator, nextValue){
    return accumulator + nextValue;
});

This will generate the following result

   accumulator    nextValue   returnedValue
    1              2             3
    3              3             6
    6              4             10
    10             5             15

And Hence the result will be 15

2. Example with adding the second parameter

var arr = [1,2,3,4,5];

arr.reduce(function(accumulator, nextValue){
    return accumulator + nextValue;
},10);

It will generate the following. Keep in mind, if the second parameter is passed then this is treated as the first value in the array

accumulator    nextValue   returnedValue
    10             1             11
    11             2             13
    13             3             16
    16             4             20
    20             5             25

There are N number of possibilities to play with .reduce()

I hope you find my answer helpful, please do like and comment it gives me the confidence to be more helpful and innovative😇