Find Sum of Array in JavaScript

What You’ll Learn

Summing an array means visiting every element once and adding it to a running total (the accumulator pattern). Example: [1, 2, 3, 4, 5] → 15. Empty arrays sum to 0; negatives are allowed. This tutorial covers a manual loop, user input, a live preview, worked JavaScript examples, edge cases, and complexity.

📝 Problem & Approach

Given an array of numbers, return the sum of all elements.

# [1, 2, 3, 4, 5] -> 15
# [10, -2, 7]     -> 15
# []              -> 0

Inputs & Outputs

Minimal workflow

function sumArray(arr) {
  let total = 0;
  for (const value of arr) {
    total += value;
  }
  return total;
}

Method comparison

🔮 Live Preview

Enter integers separated by commas or spaces and compute the sum instantly.

Press “Compute sum”.

Examples Gallery

Three complete JavaScript programs — sum a fixed array, read user-style input, and show a running total with negatives. Click View Output to reveal sample console results.

function sumArray(arr) {
  let total = 0;
  for (const value of arr) {
    total += value;
  }
  return total;
}

const array = [1, 2, 3, 4, 5];
console.log(`Sum of the array elements: ${sumArray(array)}`);

Sum of the array elements: 15

function sumArray(arr) {
  let total = 0;
  for (const value of arr) {
    total += value;
  }
  return total;
}

// Simulated input (edit these values)
const n = 5;
const arr = [1, 2, 3, 4, 5];
if (n < 0) {
  throw new Error("n must be nonnegative.");
}

console.log(`Sum of the array elements: ${sumArray(arr)}`);

Enter number of elements: 5
Enter element 1: 1
Enter element 2: 2
Enter element 3: 3
Enter element 4: 4
Enter element 5: 5
Sum of the array elements: 15

const arr = [10, -2, 7];
let total = 0;
console.log("Running total:");
for (const value of arr) {
  total += value;
  const signed = value >= 0 ? `+${value}` : String(value);
  console.log(`  after ${signed}: ${total}`);
}
console.log(`Final sum: ${total}`);

Running total:
  after +10: 10
  after -2: 8
  after +7: 15
Final sum: 15

🔎 Worked Walkthrough — [1, 2, 3, 4, 5]

Watch the accumulator climb from 0 to 15.

Same table works for [10, -2, 7]: 0 → 10 → 8 → 15.

⚖️ Facts Worth Knowing

Handy follow-ups interviewers sometimes ask.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

You must read every element, so linear time is optimal for an unsorted array.

💡 Best Practices