Microsoft continuously upgrades its products.
As earlier, we were using Outlook REST APIs OR EBS APIs
But now a days, there are many new services introduced.
E.g.,
My client has requirements to obtain the Outlook tasks. I checked. There are many approaches, but I'm not sure which one is the most recommended.
What is the best recommendation solution for a Outlook javascript-based add-in?
OfficeJs APIs are the APIs provided for web addins and you should use these whenever possible. If you do not find API for your scenario in OfficeJs APIs you can use other APIs. For these APIs you will need to acquire auth token. You can try using Microsoft Graph APIs as it's most recent. For more details on enabling SSO and acquiring Graph token for addins please check here
You can also use Office JS API(makeEwsRequestAsync) to make EWS request this would not require you to acquire access token separately. Please refer to doc here for more details