Multiply and Sum Two Arrays in JavaScript

We are required to write a JavaScript function that takes in two arrays of equal length. The function should multiply the corresponding (by index) values in each, and sum the results.

For example: If the input arrays are ?

const arr1 = [2, 3, 4, 5];
const arr2 = [4, 3, 3, 1];

then the output should be 34, because:

(2*4 + 3*3 + 4*3 + 5*1) = 8 + 9 + 12 + 5 = 34

Using for Loop

The most straightforward approach uses a for loop to iterate through both arrays simultaneously:

const arr1 = [2, 3, 4, 5];
const arr2 = [4, 3, 3, 1];

const produceAndAdd = (arr1 = [], arr2 = []) => {
    let sum = 0;
    for(let i = 0; i < arr1.length; i++) {
        const product = (arr1[i] * arr2[i]);
        sum += product;
    }
    return sum;
};

console.log(produceAndAdd(arr1, arr2));

34

Using reduce Method

A more functional approach uses the reduce method for cleaner, more readable code:

const arr1 = [2, 3, 4, 5];
const arr2 = [4, 3, 3, 1];

const multiplyAndSum = (arr1, arr2) => {
    return arr1.reduce((sum, val, index) => {
        return sum + (val * arr2[index]);
    }, 0);
};

console.log(multiplyAndSum(arr1, arr2));

34

Using map and reduce Together

This approach first maps the products, then reduces to get the sum:

const arr1 = [2, 3, 4, 5];
const arr2 = [4, 3, 3, 1];

const multiplyAndSum = (arr1, arr2) => {
    return arr1
        .map((val, index) => val * arr2[index])
        .reduce((sum, product) => sum + product, 0);
};

console.log(multiplyAndSum(arr1, arr2));
console.log("Products:", arr1.map((val, index) => val * arr2[index]));

34
Products: [ 8, 9, 12, 5 ]

Comparison

Conclusion

All methods effectively multiply corresponding array elements and sum the results. Use the for loop for performance-critical code, or reduce for cleaner functional programming style.