In this book you're going to use the ArcGIS API for JavaScript Sandbox to write and test your code. The Sandbox can be found at https://developers.arcgis.com/javascript/3/sandbox/sandbox.html and will appear as seen in the screenshot when loaded. You'll write your code in the left pane and click the REFRESH button to see the results in the right pane:
United States
Great Britain
India
Germany
France
Canada
Russia
Spain
Brazil
Australia
Singapore
Hungary
Ukraine
Luxembourg
Estonia
Lithuania
South Korea
Turkey
Switzerland
Colombia
Taiwan
Chile
Norway
Ecuador
Indonesia
New Zealand
Cyprus
Denmark
Finland
Poland
Malta
Czechia
Austria
Sweden
Italy
Egypt
Belgium
Portugal
Slovenia
Ireland
Romania
Greece
Argentina
Netherlands
Bulgaria
Latvia
South Africa
Malaysia
Japan
Slovakia
Philippines
Mexico
Thailand