JavaScript function to calculate the Mean/Average, Median, Mode, and Range in JavaScript.

``````//
// Calculating the average/mean
// https://www.sitepoint.com/community/t/calculating-the-average-mean/7302/3
//

/**
* The "mean" is the "average" you're used to, where you add up all the numbers
* and then divide by the number of numbers.
*
* For example, the "mean" of [3, 5, 4, 4, 1, 1, 2, 3] is 2.875.
*
* @param {Array} numbers An array of numbers.
* @return {Number} The calculated average (or mean) value from the specified
*     numbers.
*/
function mean(numbers) {
var total = 0, i;
for (i = 0; i < numbers.length; i += 1) {
total += numbers[i];
}
}

//
// alternative mean/average method (from https://www.30secondsofcode.org/snippet/average):
const mean = (...numbers) => numbers.reduce((acc, val) => acc + val, 0) / numbers.length;
//
// usage:
mean(...[1,2,3]); // 2
mean(...[0,1,2,3,4,5,6,7,8,9,10]); // 5
mean(...[1,2,3]); // 2

/**
* The "median" is the "middle" value in the list of numbers.
*
* @param {Array} numbers An array of numbers.
* @return {Number} The calculated median value from the specified numbers.
*/
function median(numbers) {
// median of [3, 5, 4, 4, 1, 1, 2, 3] = 3
var median = 0, numsLen = numbers.length;
numbers.sort();

if (
numsLen % 2 === 0 // is even
) {
// average of two middle numbers
median = (numbers[numsLen / 2 - 1] + numbers[numsLen / 2]) / 2;
} else { // is odd
// middle number only
median = numbers[(numsLen - 1) / 2];
}

return median;
}

/**
* The "mode" is the number that is repeated most often.
*
* For example, the "mode" of [3, 5, 4, 4, 1, 1, 2, 3] is [1, 3, 4].
*
* @param {Array} numbers An array of numbers.
* @return {Array} The mode of the specified numbers.
*/
function mode(numbers) {
// as result can be bimodal or multi-modal,
// the returned result is provided as an array
// mode of [3, 5, 4, 4, 1, 1, 2, 3] = [1, 3, 4]
var modes = [], count = [], i, number, maxIndex = 0;

for (i = 0; i < numbers.length; i += 1) {
number = numbers[i];
count[number] = (count[number] || 0) + 1;
if (count[number] > maxIndex) {
maxIndex = count[number];
}
}

for (i in count)
if (count.hasOwnProperty(i)) {
if (count[i] === maxIndex) {
modes.push(Number(i));
}
}

return modes;
}

/**
* The "range" of a list a numbers is the difference between the largest and
* smallest values.
*
* For example, the "range" of [3, 5, 4, 4, 1, 1, 2, 3] is [1, 5].
*
* @param {Array} numbers An array of numbers.
* @return {Array} The range of the specified numbers.
*/
function range(numbers) {
numbers.sort();
return [numbers[0], numbers[numbers.length - 1]];
}
``````