The Array reduceRight() method executes a reducer function for every array item, working from right to left, returning a single value representing the function’s accumulated result.

<!-- html element to place output -->
<p id="my_total"></p>

// arrays
let my_numbers = [200, 12, 18];
let my_total = my_numbers.reduceRight(my_function);

// function to run (adds numbers in array)
function my_function(total, number) {
    return total + number;
}

// output the square roots of all the array items
document.getElementById('my_total').innerHTML = 'Total: ' + my_total;

The way this works (see Syntax section below):

• The reduceRight() method cycles through the array starting from the end, doing something with the items (in this case, subtracting them)

Total: -194

array.reduce(function(total, currentValue, currentIndex, arr), initialValue)

Parameter	Description
function()	A function to be run for each element in the array (required)
total	The initialValue, or the previously returned value of the function (required)
currentValue	The value of the current element (required)
currentIndex	The index of the current element
arr	The array the current element belongs to
initialValue	A value to be passed to the function as the initial value

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