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
United Kingdom
India
Germany
France
Canada
Russia
Spain
Brazil
Australia
Argentina
Austria
Belgium
Bulgaria
Chile
Colombia
Cyprus
Czechia
Denmark
Ecuador
Egypt
Estonia
Finland
Greece
Hungary
Indonesia
Ireland
Italy
Japan
Latvia
Lithuania
Luxembourg
Malaysia
Malta
Mexico
Netherlands
New Zealand
Norway
Philippines
Poland
Portugal
Romania
Singapore
Slovakia
Slovenia
South Africa
South Korea
Sweden
Switzerland
Taiwan
Thailand
Turkey
Ukraine