The developer console is an important tool as you work on your programs. If your scripts have any errors, they often an won't execute properly. The console will display a diagnostic message in such cases. It also holds the result of any calls to console.log() made by your scripts. For these reasons, it is probably a good idea to keep the console open at all times during development and testing.
Opening the Console
On Chrome, Firefox, and Edge browsers you can open the developer tools by hitting the F12 key. If not already selected, the console should be one of the tabs provided with these tools. You can also reach the tools on these browsers from their menu. In Chrome, look for "More Tools" then "Developer Tools". In Firefox, it is "Web Developer" the "Toggle Tools". In Edge, it is just "Developer Tools".
In Safari there is an extra step needed before the tools will show up in the menu.
- Open Safari preferences
- Go to Advanced settings
- Check box for “Show Develop menu in menu bar”
- Now the Develop menu should show up
- Click on “Show JavaScript Console” in the Develop menu
(Thanks to Grace Bratzel for these instructions.)