Sum of an Array in JavaScript

There are multiple ways to calculate the sum of elements in an array in JavaScript. Here are some of the most common methods:

1. Using for loop (Simple for all Array)

A basic and straightforward way to sum the elements of an array is by using a for loop. This method iterates through each element in the array, adding it to a cumulative sum.

let a = [4, 8, 7, 13, 12]
let sum = 0;

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

• The loop goes through each element of the array.
• Each element is added to the sum variable on each iteration.

2. Using forEach() Method

forEach() method is a built-in method that allows you to run a function on each element in the array. You can use it to add up the numbers.

let a = [4, 8, 7, 13, 12]
let sum = 0;
a.forEach(x => {
    sum += x;
});
console.log(sum);

• forEach() runs the function for each item in the array.
• The function adds each number to sum.

3. Using reduce() Method

We are going to use the JavaScript reduce() method to find the sum of the array. reduce() is a more elegant way to sum up array elements. It works by processing all the array elements and combining them into a single value.

let a = [4, 8, 7, 13, 12]

let sum = a.reduce(function (x, y) {
    return x + y;
}, 0);
console.log(sum);

• reduce() starts with an initial value (0) and adds each element to it.
• It returns the final sum after processing all the elements.

4. Using Recursion

Recursion means a function calling itself until a condition is met. Here, the function adds elements until it reaches the end of the array.

let a = [4, 8, 7, 13, 12];
function sumArray(a, idx) {
    if (idx === a.length) {
        return 0;
    }
    return a[idx] + sumArray(a, idx + 1);
}
console.log(sumArray(a, 0));

• The function keeps calling itself with the next index.
• When it reaches the end, it returns 0, and the values are added back together.

5. UsingLodash _.sum() Method

In this approach, we are using the Lodash _.sum() method for getting the sum of all element of an array.

// Requiring the lodash library 
const _ = require("lodash");

// Use of _.sum () method 
let sum = _.sum([5, 10, 15, 20, 25]);
console.log(sum);

• _.sum() automatically adds up all the numbers in the array and returns the sum.

6. Using the eval Function

The eval Function approach calculates the sum of an array by converting it to a string with elements joined by '+', then using eval to evaluate the string as a JavaScript expression, returning the sum.

const sum = a => eval(a.join('+'));
const a = [1, 2, 3, 4, 5];
console.log(sum(a)); 

• The array is joined into a string like "1+2+3+4+5".
• eval() runs the string as a math expression and returns the sum.

Note: This method can be dangerous because eval() can execute any code in the string.

7. Using the map() Method with reduce()

While map() is usually for transforming data, you can combine it with reduce() to sum the elements. However, it’s a bit less efficient because it creates a new array.

let numbers = [1, 2, 3, 4, 5];

let sumUsingMap = numbers.map(num => num).reduce((acc, curr) => acc + curr, 0);

console.log(sumUsingMap);

• map() creates a new array with the same elements.
• reduce() then sums up the values of the new array.

Conclusion

If you're a beginner and come from another programming language, the simple for loop is a good choice because it’s easy to understand. But if you're working with JavaScript, it's helpful to know methods like map(), reduce(), and forEach(). These methods are more efficient and make your code cleaner, which is important as you get more comfortable with JavaScript.