Retrieve Function Arguments with nthArg

Introduction

In this lab, we will explore the implementation of a JavaScript function called nthArg, which allows us to retrieve the nth argument of a function. We will learn how to use Array.prototype.slice() method to retrieve the desired argument, and also how to handle negative values for n. By the end of this lab, we will have a solid understanding of how to use nthArg to retrieve arguments from a function.

A function that gets the nth argument

To start practicing coding, open the Terminal/SSH and type node. Here's how you can create a function that gets the argument at index n.

• Use Array.prototype.slice() to get the desired argument at index n.
• If n is negative, the nth argument from the end is returned.

const nthArg =
  (n) =>
  (...args) =>
    args.slice(n)[0];

Here's an example of how to use the nthArg function:

const third = nthArg(2);
console.log(third(1, 2, 3)); // Output: 3
console.log(third(1, 2)); // Output: undefined

const last = nthArg(-1);
console.log(last(1, 2, 3, 4, 5)); // Output: 5

Summary

Congratulations! You have completed the NTH Argument lab. You can practice more labs in LabEx to improve your skills.