Sum of Array Elements

Program to calculate sum of all array elements

BeginnerTopic: Array Programs

JavaScript Sum of Array Elements Program

This program helps you to learn the fundamental structure and syntax of JavaScript programming.

// Method 1: Using for loop
function sumArray(arr) {
    let sum = 0;
    for (let i = 0; i < arr.length; i++) {
        sum += arr[i];
    }
    return sum;
}

let numbers = [1, 2, 3, 4, 5];
console.log("Array:", numbers);
console.log("Sum:", sumArray(numbers));

// Method 2: Using reduce
function sumArrayReduce(arr) {
    return arr.reduce((acc, num) => acc + num, 0);
}

console.log("\nUsing reduce:", sumArrayReduce([10, 20, 30]));

// Method 3: Using forEach
function sumArrayForEach(arr) {
    let sum = 0;
    arr.forEach(num => sum += num);
    return sum;
}

console.log("\nUsing forEach:", sumArrayForEach([5, 10, 15]));

// Method 4: Using for...of loop
function sumArrayForOf(arr) {
    let sum = 0;
    for (let num of arr) {
        sum += num;
    }
    return sum;
}

console.log("\nUsing for...of:", sumArrayForOf([2, 4, 6, 8]));

// Method 5: One-liner
const sum = arr => arr.reduce((a, b) => a + b, 0);

console.log("\nOne-liner:", sum([1, 2, 3, 4, 5]));

// Method 6: Sum with condition (even numbers only)
function sumEvenNumbers(arr) {
    return arr.filter(num => num % 2 === 0)
              .reduce((acc, num) => acc + num, 0);
}

console.log("\nSum of even numbers:", sumEvenNumbers([1, 2, 3, 4, 5, 6]));

Output

Array: [ 1, 2, 3, 4, 5 ]
Sum: 15

Using reduce: 60

Using forEach: 30

Using for...of: 20

One-liner: 15

Sum of even numbers: 12

Understanding Sum of Array Elements

This program demonstrates different methods to sum array elements.

Method 1: For Loop

Traditional approach:

let sum = 0;
for (let i = 0; i < arr.length; i++) {
    sum += arr[i];
}

Method 2: Reduce

Most common modern approach:

arr.reduce((acc, num) => acc + num, 0);

Initial Value:

•0 is the starting accumulator value

•Important for empty arrays

Method 3: ForEach

Functional iteration:

let sum = 0;
arr.forEach(num => sum += num);

Method 4: For...Of Loop

ES6 iteration:

for (let num of arr) {
    sum += num;
}

For...Of vs For Loop:

•For...of: Cleaner, works with any iterable

•For loop: More control, index access

Method 5: Arrow Function

One-liner:

const sum = arr => arr.reduce((a, b) => a + b, 0);

Method 6: Conditional Sum

Sum only even numbers:

arr.filter(num => num % 2 === 0)
   .reduce((acc, num) => acc + num, 0);

Chaining Methods:

•filter(): Creates new array with matching elements

•reduce(): Sums filtered array

Performance:

•All methods: O(n) time complexity

•Reduce: Slightly more efficient (single pass)

When to Use:

Reduce

: Most common, functional

For loop

: Learning, custom logic

For...of

: Clean iteration

One-liner

: Quick calculations

Let us now understand every line and the components of the above program.

Note: To write and run JavaScript programs, you need to set up the local environment on your computer. Refer to the complete article Setting up JavaScript Development Environment. If you do not want to set up the local environment on your computer, you can also use online IDE to write and run your JavaScript programs.

Practical Learning Notes for Sum of Array Elements

This JavaScript program is part of the "Array Programs" topic and is designed to help you build real problem-solving confidence, not just memorize syntax. Start by understanding the goal of the program in plain language, then trace the logic line by line with a custom input of your own. Once you can predict the output before running the code, your understanding becomes much stronger.

A reliable practice pattern is to run the original version first, then modify only one condition or variable at a time. Observe how that single change affects control flow and output. This deliberate style helps you understand loops, conditions, and data movement much faster than copying full solutions repeatedly.

For interview preparation, explain this solution in three layers: the high-level approach, the step-by-step execution, and the time-space tradeoff. If you can teach these three layers clearly, you are ready to solve close variations of this problem under time pressure.

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