JavaScript Program to Find Sum of Array Elements

You can find the sum of an array in JavaScript using array.reduce((acc, val) => acc + val, 0), which adds all elements starting from zero.

Examples

Input[1, 2, 3]

Output6

Input[10, -5, 7, 3]

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 to a total starting at zero. You go through the list from start to end, adding each number to your total until you finish all numbers.

Algorithm

1

Start with a total sum set to zero.

2

Look at each number in the array one by one.

3

Add the current number to the total sum.

4

After all numbers are added, 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] through the code to see how the sum is calculated.

1

Initialize sum

Start with acc = 0

2

Add first element

acc = 0 + 1 = 1

3

Add second element

acc = 1 + 2 = 3

4

Add third element

acc = 3 + 3 = 6

5

Return result

Sum is 6

Accumulator (acc)
0
1
3
6

Why This Works

Step 1: Start with zero

We begin adding from zero because zero is the neutral number for addition, so it doesn't change the sum.

Step 2: Add each element

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

Step 3: Use reduce method

The reduce method loops through the array and keeps updating the total sum automatically.

Alternative Approaches

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 is a simple and clear way but requires more lines than reduce.

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 more readable than a classic for loop and easy to understand.

while loop

javascript

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

Works fine but less common for this task compared to for loops.

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 array size.

Space Complexity

Only a few variables are used for the sum and counters, so space stays constant regardless of array size.

Which Approach is Fastest?

All methods have similar speed since they all add each element once; reduce is concise but for loops are equally efficient.

Approach	Time	Space	Best For
reduce	O(n)	O(1)	Concise functional style
for loop	O(n)	O(1)	Classic and explicit control
for...of loop	O(n)	O(1)	Readable iteration
while loop	O(n)	O(1)	Less common, manual control