JavaScript Program to Find Sum of Array Elements

You can find the sum of array elements in JavaScript by using array.reduce((acc, val) => acc + val, 0) which adds all numbers together.

Examples

Input[1, 2, 3, 4, 5]

Output15

Input[10, -2, 7, 0]

Output15

Input[]

Output0

How to Think About It

To find the sum of numbers in an array, think of adding each number one by one starting from zero. You keep a running total and add each element to it until you reach the end of the array.

Algorithm

1

Start with a total sum set to zero.

2

Go through each element in the array one by one.

3

Add the current element's value to the total sum.

4

After processing all elements, return the total sum.

Code

javascript

const numbers = [1, 2, 3, 4, 5];
const sum = numbers.reduce((acc, val) => acc + val, 0);
console.log(sum);

Output

15

Dry Run

Let's trace the array [1, 2, 3, 4, 5] through the code to see how the sum is calculated.

1

Initialize sum

sum starts at 0

2

Add first element

sum = 0 + 1 = 1

3

Add second element

sum = 1 + 2 = 3

4

Add third element

sum = 3 + 3 = 6

5

Add fourth element

sum = 6 + 4 = 10

6

Add fifth element

sum = 10 + 5 = 15

Current sum after adding element
1
3
6
10
15

Why This Works

Step 1: Starting with zero

We begin with a total sum of 0 because adding zero does not change the sum.

Step 2: Adding each element

Each element in the array is added to the running total using the + operator.

Step 3: Using reduce method

The reduce method applies a function that accumulates the sum by processing each element in order.

Alternative Approaches

Using a for loop

javascript

const numbers = [1, 2, 3, 4, 5];
let sum = 0;
for (let i = 0; i < numbers.length; i++) {
  sum += numbers[i];
}
console.log(sum);

This method is straightforward and easy to understand but requires more lines of code.

Using for...of loop

javascript

const numbers = [1, 2, 3, 4, 5];
let sum = 0;
for (const num of numbers) {
  sum += num;
}
console.log(sum);

This is a cleaner loop syntax that is easy to read and write.

Complexity: O(n) time, O(1) space

Time Complexity

The program visits each element once to add it, so the time grows linearly with the number of elements.

Space Complexity

Only a single variable is used to keep the sum, so extra memory use is constant.

Which Approach is Fastest?

All methods have similar time and space complexity; reduce is concise, while loops may be more explicit.

Approach	Time	Space	Best For
reduce method	O(n)	O(1)	Concise functional code
for loop	O(n)	O(1)	Explicit control and clarity
for...of loop	O(n)	O(1)	Readable and modern syntax