How do you describe the interaction between frontend and backend when designing an API?

Interaction between frontend and backend when designing APIs is based on clear separation of responsibilities and standardization of data exchange. Typically, an API is designed as a set of endpoints that the frontend calls to retrieve or send data.

Key points:

• Contract Definition: clearly describing request and response formats (e.g., JSON), data structure, mandatory and optional fields.
• REST or GraphQL: choosing the appropriate API style, REST being the most common, where resources are identified by URLs and operations by HTTP methods.
• Authentication and Authorization: describing security mechanisms, such as OAuth, JWT.
• Error Handling: standardizing error codes and messages so that the frontend can respond correctly.
• API Versioning: to avoid breaking existing frontend when making changes.

Example of a simple REST API to get a list of users:

GET /api/users HTTP/1.1
Host: example.com
Accept: application/json

--- Response ---
HTTP/1.1 200 OK
Content-Type: application/json

[
  {"id":1, "name":"Ivan"},
  {"id":2, "name":"Maria"}
]

Thus, the frontend knows how and what to request, and the backend ensures stability and predictability of responses.