Answers

1. It depends on the use cases. However, GraphQL performs much better for mobile apps and web-based UI applications and is best suited for service-to-service (s2s) communications.
2. Fragments should be used while sending a request from the GraphQL client when the response contains an interface or union.
3. You can use a variable in a GraphQL query/mutation, as shown in the following code. This code used to modify the GraphQL request sent in step 6 of the Testing GraphQL queries and mutations section:

   mutation {  addStar(input: {starrableId: $repoId }) {    clientMutationId  }}

Here, you can see that the $repoId variable is used. You must declare that variable in the named mutation and it can then be used in the mutation’s argument, as shown in the following code snippet:

{  "repoId": "R_kgDOHzYNwg"
}