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Comments

Part of the Fundamentals section of Coddy's JavaScript journey — lesson 3 of 77.

Comments are notes you write inside your code. JavaScript completely ignores them - they exist only to help humans understand the code.

To write a single-line comment, use //. Everything after // until the end of the line is ignored:

// This is a comment
console.log("Hello!")

A comment can also be written at the end of a line, after the code:

console.log("Hello!") // This prints Hello!

For comments that span several lines, use /* to start and */ to end:

/* This is a multi-line comment.
   JavaScript ignores all of it. */
console.log("Welcome!")

Comments can also temporarily disable a line of code without deleting it:

// console.log("This line will NOT run")
console.log("This line will run")
challenge icon

Challenge

Beginner

Fix the code so that only Hello, JavaScript! is printed.

  • Replace the ? with the symbols that turn a line into a comment
  • The line printing Goodbye! should become a comment so it does NOT run
  • Only change the line that starts with ?

Cheat sheet

Comments in JavaScript:

  • Notes for humans - JavaScript ignores them
  • Can disable code temporarily without deleting it

Single-line comment:

// This is a comment
console.log("Hello!") // Comment after code

Multi-line comment:

/* This is a
   multi-line comment */

Disabling code:

// console.log("This will NOT run")
console.log("This will run")

Try it yourself

// Type your code below
? console.log("Goodbye!")
console.log("Hello, JavaScript!")
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