An array in JavaScript is an object that allows you to store an ordered collection of multiple values under a single variable name and manipulate those values in numerous ways.

In this article, you will learn how to calculate the sum of all the numbers in a given array using a few different approaches.

Specifically, I will show you how to find the sum of all numbers in an array by using:

  • A for loop
  • The forEach() method
  • The reduce() method

Let's get started!

How to Calculate the Sum of an Array Using A for Loop in JavaScript

One of the simplest ways of calculating the sum of all numbers in an array is using a for loop. It performs an iteration n number of times.

Let's look at the following example:

// create an array
let myNums = [1, 2, 3, 4, 5];

// create a variable for the sum and initialize it
let sum = 0;

// iterate over each item in the array
for (let i = 0; i < myNums.length; i++ ) {
  sum += myNums[i];
}

console.log(sum) // 15

In the example above, I first created an array named myNums that stores five values.

I then declared a variable named sum and initialized it with a value of 0 – this variable will store the result from the calculations in the for loop.

Next, I used the for loop to iterate over all the elements until the end of the myNums array.

I also reassigned the value of the sum variable using the addition assignment operator by adding its current value and the current array element.

To learn more about the for loop in JavaScript, give this article a read.

How to Calculate the Sum of an Array Using the forEach() Method in JavaScript

Another way to calculate the sum of an array is using JavaScript's built-in forEach() method. It iterates over an array and calls a function for each item.

Let's look at the following example:

// create an array
const myNums = [1,2,3,4,5];

// create a variable for the sum and initialize it
let sum = 0;

// calculate sum using forEach() method
myNums.forEach( num => {
  sum += num;
})

console.log(sum) // 15

In the example above, I created an array myNums. I also declared a variable named sum and initialized it with a value of 0.

Then, I used the forEach() method to iterate over each item in the array.

On each iteration, I reassigned the value of the sum variable by adding its current value and the value of the current array element in each iteration.

To learn more about the forEach() function, give this article a read.

How to Calculate the Sum of an Array Using the reduce() Method in JavaScript

Another way of calculating the sum of an array is using the reduce() method, which got introduced with ES6.

The reduce() method reduces all elements in an array into a single value.

Let's look at the following example:

// create an array
const myNums = [1,2,3,4,5];

// use reduce() method to find the sum
var sum = myNums.reduce((accumulator, currentValue) => {
  return accumulator + currentValue
},0);

console.log(sum) // 15

The reduce() method takes a user-defined callback function as its first required argument. The function gets called on each element in the array.

The callback function accepts the following two required parameters:

  • The accumulator, which is the variable that stores the last returned value from the previous function call.
  • The currentValue, which represents the current array item.

The second argument to the reduce() method is the initialValue, which is 0. The initialValue represents the initial value of the accumulator.

To learn more about the reduce() method, give this article a read.

Conclusion

And there you have it! You have learned three ways to calculate the sum of an array in JavaScript.

To learn more about JavaScript, check out this Full JavaScript Course for Beginners.

Thanks for reading, and happy coding!