Membership Testing

Part of the Fundamentals section of Coddy's JavaScript journey — lesson 70 of 77.

You can check whether an element is in an array or not using the indexOf() method:

const arr = ["a", "b", "c"];
console.log(arr.indexOf("b")); // Output: 1
console.log(arr.indexOf("d")); // Output: -1

If the element is not found, indexOf() returns -1.

You can also use the includes() method that was learned before!

Challenge

Easy

Create a program that receives two arrays of numbers as input (given) and prints a new array of all elements that are in the first array but NOT in the second array.

Cheat sheet

Use indexOf() to check if an element exists in an array:

const arr = ["a", "b", "c"];
console.log(arr.indexOf("b")); // Output: 1
console.log(arr.indexOf("d")); // Output: -1

If the element is not found, indexOf() returns -1.

Try it yourself

let arr1 = inp[0].split(", ").map(Number);
let arr2 = inp[1].split(", ").map(Number);
// Write your code below

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Fundamentals

1Introduction

The Language Hello World!Comments Code Structure

4Operators Part 2

Logical Operators Part 1 Logical Operators Part 2 Recap - Simple Logic Logical Operators Part 3 Type Coercion

7Bill Split Calculator

Welcome Message Calculating The Tip And Total

Splitting The Bill

Formatted Output

10FizzBuzz with a Twist

Game Overview The FizzBuzz Function

Looping The Numbers

Adding The Twist

13Grocery List Tracker

Project Overview Add Item

Remove Item

View List