Find the Average of a Given Array of Numbers

Find the average of all numbers in a given array

Let's say we wanted to write a function that calculates the average of all grades (including yours). We can do this in many different ways in JavaScript, but in this demo I will be showing you how to find the average using Higher-Order Functions and the "for" loop.

forEach loop

The forEach() method executes a provided function once for each array element.

const yourGrade = 88;
let classGrades = [
    87, 68, 94, 100, 83,
    78, 85, 91, 76, 87
];

// push `yourGrade` to the end of classGrades
classGrades.push(yourGrade);
console.log(classGrades);

function average(array) {
  // initialize value of `sum`
  let sum = 0;
  // capture the length of the array
  let arrayLength = array.length;
  // loop through the array via forEach
  array.forEach((grade) => {
    return (sum += grade);
  });
  // formula to calculate average: sum / arrayLength
  return Math.round(sum / arrayLength);
}
const avg = average(classGrades);
console.log(avg);

for loop

The for() loop iterates a specified amount of times, and does "something" that many times.

const yourGrade = 88;
let classGrades = [
    87, 68, 94, 100, 83,
    78, 85, 91, 76, 87
];

console.log(classGrades);

function average(array) {
  // initialize value of `sum`
  let sum = 0;
  // capture the length of the array
  let arrayLength = array.length;
  // iterate over the array
  for (let i = 0; i < array.length; i++) {
    // add each element to the `sum`
    sum += array[i];
  }
  // formula to calculate average: sum / arrayLength
  /* since we are not pushing our grade to the array
   using `array.push()`, we need to do a little bit of algebra
   to add ourselves to the list */
  return Math.round((sum + yourGrade) / (arrayLength + 1));
}
const avg = average(classGrades);
console.log(avg);

reduce

The reduce() method is quite similar to the forEach() method, but requires a lot less coding. :)

const yourGrade = 88;
let classGrades = [
    87, 68, 94, 100, 83,
    78, 85, 91, 76, 87
];

// push `yourGrade` to the end of classGrades
classGrades.push(yourGrade);
console.log(classGrades);

function average(array) {
    // action to do for every value
  const avg =
    array.reduce((previousValue, currentValue) =>
    previousValue + currentValue) / array.length;
  return Math.round(avg);
}
const avg = average(classGrades);
console.log(avg);