Response envelope patterns in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this JSON response envelope?

Consider this API response envelope pattern:

{
  "status": "success",
  "data": {
    "user": {
      "id": 101,
      "name": "Alice"
    }
  },
  "error": null
}

What will be the value of error in this response?

A "null" (string)

B An empty object {}

C An empty string ""

D null (JSON null value)

💡 Hint

Look carefully at the value type of error in the JSON.

The error field is set to null which is a JSON null value, not a string or empty object.

🧠 Conceptual

intermediate

Why use a response envelope in REST APIs?

Which of the following is the main reason to use a response envelope pattern in REST APIs?

A To separate metadata like status and errors from the actual data payload

B To make the response smaller by removing metadata

C To always return HTTP status 200 and put error info inside the envelope

D To force clients to parse XML instead of JSON

💡 Hint

Think about how metadata and data are organized in the response.

Response envelopes separate metadata (status, errors) from the main data, making responses consistent and easier to handle.

🔧 Debug

advanced

Identify the error in this response envelope example

Here is a JSON response envelope from an API:

{
  "status": "error",
  "data": null,
  "error": {
    "code": 404,
    "message": "User not found"
  }
}

What is wrong with this response if the HTTP status code is also 404?

A The <code>data</code> field should not be null when there is an error

B The <code>status</code> field should be "success" even if HTTP status is 404

C There is no error; this is a correct pattern

D The HTTP status code should be 200 when using response envelopes

💡 Hint

Think about how error information is represented in the envelope and HTTP status.

It is valid to return HTTP 404 with an error envelope showing the error details and data as null.

📝 Syntax

advanced

Which JSON response envelope is syntactically correct?

Choose the syntactically correct JSON response envelope:

A { "status": "success", "data": { "id": 1, "name": "Bob" }, "error": null }

B { "status": "success", "data": { "id": 1, "name": "Bob" }, "error": }

C { "status": "success", "data": { "id": 1, "name": "Bob" }, "error": undefined }

D { "status": "success", "data": { "id": 1, "name": "Bob" }, "error": None }

💡 Hint

Remember JSON syntax rules for null and values.

Only option A uses valid JSON syntax with null for no error. Options A, C, and D are invalid JSON.

🚀 Application

expert

How many items are in the 'data' field of this response envelope?

Given this JSON response envelope:

{
  "status": "success",
  "data": {
    "users": [
      {"id": 1, "name": "Anna"},
      {"id": 2, "name": "Ben"},
      {"id": 3, "name": "Cara"}
    ],
    "count": 3
  },
  "error": null
}

How many user objects are inside the data.users array?

A 2

B 3

C 4

D 0

💡 Hint

Count the number of objects inside the users array.

The users array contains exactly 3 user objects.