In order to develop applications with the ArcGIS API for JavaScript, you need to join the ArcGIS Developer Program or have an ArcGIS Online account.
While you are developing and testing your application, you can use the free Essentials Plan of the ArcGIS Developer Subscription. Before deploying your app in production, you will need to ensure that your application meets one of the following requirements:
As long as one of the above criteria is met, no additional licensing is required when deploying apps built with the ArcGIS API for JavaScript to production.
To learn more, check out the full ArcGIS Terms of Use and the Terms of Use FAQ.
Esri requires that when you use an ArcGIS Online basemap, Esri data services, or Esri API technology in your app you must also include Esri attribution. There are specific requirements for attribution you may be required to address in your app depending on how your app is built and the data it uses.
When building your app with the ArcGIS API for JavaScript, both data and Esri attribution can easily be handled using the default implementation at the bottom of the map. This is the recommended placement, so apply it there if it works with your app design.
More information on attribution requirements can be found on the Attribution in your app page.