Implement Infinite Currying Sum: JavaScript Interview Question sum(1)(2)(3)

Infinite currying sum and multiplication are one of the best examples to check the understanding of currying and its implementation to generate partial functions. In this post, we will going to cover the infinite currying sum implementation.

Table of Contents

1. Implementing Infinite Currying Sum
2. Real-world example

Implementing Infinite Currying Sum

Let's start by implementing a function that can take any number of arguments and return the sum of all those arguments. We will use currying to achieve this.

Step 1: Define the Base Function

function sum(...args) {
    return args.reduce((acc, val) => acc + val, 0);
}

The above function takes any number of arguments using the rest parameter syntax (...args) and uses the reduce method to sum them up.

Step 2: Implement Currying

function curry(func) {
    return function curried(...args) {
        if (args.length >= func.length) {
            return func(...args);
        } else {
            return function (...nextArgs) {
                return curried(...args, ...nextArgs);
            };
        }
    };
}

const curriedSum = curry(sum);

In the curry function, we check if the number of arguments passed is equal to or greater than the number of arguments expected by the sum function. If not, we return a new function that takes the remaining arguments. This process continues until all arguments are collected and the sum is calculated.

Step 3: Using Infinite Currying

console.log(curriedSum(1)(2)(3)()); // Output: 6
console.log(curriedSum(5)(10)(15)(20)()); // Output: 50

By invoking the curriedSum function with a series of arguments followed by an empty function call, we can achieve infinite currying and calculate the sum of all the arguments provided.

Real-World Example

Let's consider a real-world scenario where currying can be useful. Suppose in the e-commerce application, we have a function that calculates the total price of a shopping cart with discounts applied based on the customer's membership level:

function calculateTotalPrice(discount) {
    return function (price) {
        return price - price * discount;
    };
}

const standardMemberPrice = calculateTotalPrice(0.1);
const premiumMemberPrice = calculateTotalPrice(0.2);

console.log(standardMemberPrice(100)); // Output: 90
console.log(premiumMemberPrice(100)); // Output: 80

In this example, the calculateTotalPrice function returns a new function that calculates the final price after applying the discount based on the membership level. This demonstrates how currying can be used to create specialized versions of a generic function.

Final Thoughts

Implementing infinite currying in JavaScript can be a powerful technique to create flexible and reusable functions. By breaking down functions into smaller units that can be partially applied, developers can achieve more expressive and concise code.

Understanding currying is not only important for technical interviews but also for writing clean and maintainable code in frontend development.

Learn Next

✅ Implement Currying Multiplication