Array Sum
Calculate the sum of all elements in a JavaScript array.
Array summation in JavaScript demonstrates the power of functional programming with reduce(). This exercise teaches you how to aggregate values and understand the accumulator pattern in modern JavaScript.
📚 Concepts & Theory
Calculating the sum of array elements is a fundamental operation in JavaScript. Unlike Python, JavaScript offers several modern functional programming methods alongside traditional loops.
Understanding Array Summation in JavaScript:
Method 1: reduce() - Most Functional
The reduce() method is the standard functional approach for aggregation:
const numbers = [1, 2, 3, 4, 5];
const sum = numbers.reduce((accumulator, current) => accumulator + current, 0);
// Returns: 15Method 2: forEach() Loop
let sum = 0;
numbers.forEach(num => sum += num);Method 3: Traditional for Loop
let sum = 0;
for (let i = 0; i < numbers.length; i++) {
sum += numbers[i];
}Method 4: for...of Loop (ES6+)
let sum = 0;
for (const num of numbers) {
sum += num;
}Understanding reduce():
- First parameter: accumulator (running total)
- Second parameter: current value being processed
- Second argument to reduce: initial value (0 in this case)
- Functional programming style
- More concise and expressive
- Chainable with other array methods
- Immutable approach (doesn't modify external variables)
array.reduce((acc, val) => acc + val, 0)🎯 Your Challenge
Write a function arraySum that returns the sum.
📝 Starter Code
function arraySum(arr) {
// Your code here
}
console.log(arraySum([1, 2, 3, 4, 5]));- Use the reduce() method for array aggregation
- The first parameter is the accumulator (running total)
- The second parameter is the current element
- Don't forget the initial value (0) as second argument to reduce
- The arrow function should return accumulator + current
Solution
function arraySum(arr) {
let total = 0;
for (let num of arr) {
total += num;
}
return total;
}
console.log(arraySum([1, 2, 3, 4, 5]));Explanation
This solution uses the reduce() method, which iterates through the array while maintaining an accumulator value. The arrow function (acc, num) => acc + num adds each number to the running total. The second argument (0) sets the initial accumulator value. This functional approach is more concise than loops and expresses the intent clearly: "reduce this array to a single sum value". Time complexity: O(n). Space complexity: O(1).
⚠️ Common Mistakes to Avoid
- Forgetting the initial value in reduce() (can cause undefined)
- Not returning the accumulator in reduce function
- Modifying the array while iterating
- Using map() instead of reduce() (map transforms, reduce aggregates)
- Confusing accumulator and current value parameters