Product of an Array in JS or JavaScript

We will be given an initial array and we have to multiply all the elements of the array with each other to find a final product.

Examples:

Input: arr = [1, 2, 3, 4, 5];
Output: 120
Explanation: 1 * 2 * 3 * 4 * 5 = 120

Input: arr = [11, 12, 13, 14, 15]
Output: 360360
Explanation: 11 * 12 * 13 * 14 * 15 = 360360

For Loop

In this method, we will use a simple for loop in JavaScript to iterate through the elements of the array and multiply them with each other to get the multiply result at the end.

const arr1 = [8, 9, 3, 7, 5, 13];
const arr2 = [12, 9, 5, 18, 23];

const iterativeMultiply = (arr) => {
    let result = 1;
    for (let i = 0; i < arr.length; i++) {
        result *= arr[i];
    }
    return result;
};

console.log(iterativeMultiply(arr1))

98280
223560

Using the Math Object:

JavaScript's Math object provides several methods for mathematical operations. We can use the Math object to multiply all the elements of an array using the Math.pow() method, which calculates the power of a number.

function multiplyArray(arr) {
    return arr.reduce((acc, curr) => acc * curr, 1);
}

const array = [1, 2, 3, 4, 5];
console.log(multiplyArray(array));

120

Using the in-built methods:

There are some in-built array methods available in JavaScript which we can use to iterate through the array elements and make changes in their values by passing a callback function inside them. We will use the map() and the reduce() in-built methods in this approach to multiply the elements of an array.

let arr1 = [8, 9, 3, 7, 5, 13];
let arr2 = [12, 9, 5, 18, 23];

let mapRes = 1;
arr1.map((currItem) => {
    mapRes *= currItem;
});

const reduceRes = arr2.reduce((res, currItem) => res *= currItem);

console.log(mapRes);
console.log(reduceRes);

98280
223560

Using forEach method

In this approach we use forEach method. With forEach we look at each number in the array, one after the other. for each number we multiply it with a running total.

function multiplyArray(arr) {
    let result = 1;
    arr.forEach(num => {
        result *= num;
    });
    return result;
}

let array = [1, 2, 3, 4, 5];
console.log(multiplyArray(array));

120

Using every() Method:

In this approach, we will use the every() method to iterate through the array. This method is typically used for testing conditions, but we can repurpose it for side-effect operations by keeping a running total and multiplying each element of the array to the running total.

const arr1 = [8, 9, 3, 7, 5, 13];
const arr2 = [12, 9, 5, 18, 23];

const everyMultiply = (arr) => {
    let result = 1;
    arr.every(num => {
        result *= num;
        return true; // Continue to the next element
    });
    return result;
};

console.log(everyMultiply(arr1)); // 98280
console.log(everyMultiply(arr2)); // 223560

98280
223560

Using the reduce Method with Initial Value

The reduce method in JavaScript can efficiently multiply all elements of an array by accumulating the product of elements. By passing an initial value to reduce, you ensure that the accumulation starts correctly. This method is concise and leverages JavaScript's built-in functionalities for array manipulation.

Example Code:

function multiplyArrayElements(arr) {
  return arr.reduce((accumulator, currentValue) => accumulator * currentValue, 1);
}

console.log(multiplyArrayElements([1, 2, 3, 4, 5]));
console.log(multiplyArrayElements([11, 12, 13, 14, 15]));

120
360360

Recursive Method - Not Recommend

In this approach, we will recursively visit each element of the array and multiply it with the product of all the previous elements to get a new product value till the current element.

const arr1 = [8, 9, 3, 7, 5, 13];
const arr2 = [12, 9, 5, 18, 23];

const recursiveMultiply = (arr, ind) => {
    if (ind === arr.length - 1) {
        return arr[ind];
    } else {
        return arr[ind] * recursiveMultiply(arr, ind + 1);
    }
};

console.log(recursiveMultiply(arr1, 0));
console.log(recursiveMultiply(arr2, 0));

98280
223560