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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 icon

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.

Try it yourself

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

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

All lessons in Fundamentals

1Introduction

The LanguageHello World!CommentsCode Structure

4Operators Part 2

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

7Bill Split Calculator

Welcome MessageCalculating The Tip And TotalProject lessonSplitting The BillProject lessonFormatted OutputProject lesson

10FizzBuzz with a Twist

Game OverviewThe FizzBuzz FunctionProject lessonLooping The NumbersProject lessonAdding The TwistProject lesson

13Grocery List Tracker

Project OverviewAdd ItemProject lessonRemove ItemProject lessonView ListProject lesson

2Variables

NumbersStringBooleanNaming ConventionsEmpty VariablesRecap - Initialize VariablesConstants

5Decision Making

If StatementIf - ElseRecap - Simple CalculatorNested If - ElseSwitch Statement

8Loops

For LoopWhile LoopBreakContinueRecap - FactorialDo While LoopNested Loop

11Arrays Part 1

Declaring an ArrayAccessing Array ElementsModifying ArraysArray Methods Part 1Array Methods Part 2Recap - Array Processor

14Final Challenges

Number PyramidDouble The OddsWhat To Buy

3Operators Part 1

Arithmetic OperatorsModulo OperatorArithmetic ShortcutsComparison OperatorsStrict vs Loose EqualityRecap - Simple Math

6Basic IO

OutputOutput with VariablesType Conversion - Part 1Type Conversion - Part 2Recap - Till 120Recap - True or False

9Functions

Declare a FunctionArgumentsReturnRecap - Sigma FunctionFunction ExpressionDefault ParametersArrow FunctionsRecap - Validation Function

12Arrays Part 2

Iterating Over ArraysThe forEach Methodfor...of LoopRecap - P CounterArray SlicingArray Methods Part 3Array Methods Part 4Membership Testing

Practice on your own: Online JavaScript compiler