JavaScript / Getting started

Printing to the console

Write your first program that prints text, see what an error looks like, and leave notes with comments.

A program is a list of instructions the computer follows from top to bottom. We write it in the editor, and the result appears in the console.

To print text, write console.log followed by the text in quotes inside brackets. Change the text, then press Run:

JavaScript 
console.log("Hello");
console.log("Good morning");
Console
Hello
Good morning
Each line ends with a semicolon ;. Text must be inside quotes, otherwise you get an error:
JavaScript 
console.log(Good luck);
Console
SyntaxError: missing ) after argument list

Comments

A line that starts with // is a comment: a note for you that the computer ignores. It is also handy for switching a line off without deleting it.

JavaScript 
// Shopping list
console.log("Eggs");
// console.log("Apple");
console.log("Milk");
Console
Eggs
Milk

Practice

1Write the programCurriculum practice

Print Good night in the console.

JavaScript Ctrl/⌘ + Enter to run · Esc then Tab to leave the editor 
  
 
Console
 
Press Run to see the result.
 
   
 
 
2Edit the programCurriculum practice
 
This program shows an error. Fix it so it prints Good luck.
 
HintText needs quotes around it.
 
 
 JavaScript Ctrl/⌘ + Enter to run · Esc then Tab to leave the editor     
 
console.log(Good luck);
  
 
Console
 
Press Run to see the result.
 
   
 
 
3Edit the programCurriculum practice
 
Turn the line that prints Fish into a comment so it is not printed.
  
 
 JavaScript Ctrl/⌘ + Enter to run · Esc then Tab to leave the editor     
 
console.log("Lion");
console.log("Fish");
console.log("Elephant");
  
 
Console
 
Press Run to see the result.
 
   
 
 
4Write the programExtra practice
 
Print your name on the first line and your city on the second. (The solution uses Mona and Cairo.)
  
 
 JavaScript Ctrl/⌘ + Enter to run · Esc then Tab to leave the editor     
 
  
 
Console
 
Press Run to see the result.
 
   
 
 
5Write the programExtra practice
 
Print this shape on three lines:
*
**
***
  
 
 JavaScript Ctrl/⌘ + Enter to run · Esc then Tab to leave the editor     
 
  
 
Console
 
Press Run to see the result.
 
   
 
 
Key points
  • console.log("text"); prints text in the console.
  • Text goes inside quotes, and each line ends with ;.
  • // starts a comment the computer ignores.