Error handling on client in GraphQL - Step-by-Step Execution

Concept Flow - Error handling on client

Send GraphQL Query

↓

Receive Response

↓

Check for Errors?

No→Process Data

Yes↓

Handle Error

↓

Show Message or Retry

The client sends a query, receives a response, checks for errors, and either processes data or handles errors accordingly.

Execution Sample

GraphQL

query GetUser {
  user(id: "1") {
    name
  }
}

// Client checks response for errors

This GraphQL query requests a user's name by ID; the client then checks if the response has errors before using the data.

Execution Table

Step	Action	Response Content	Error Present?	Client Action	Output
1	Send query to server	N/A	N/A	Waiting for response	No output yet
2	Receive response	{"data":{"user":{"name":"Alice"}}}	No	Process data	Display user name: Alice
3	Send query to server	N/A	N/A	Waiting for response	No output yet
4	Receive response	{"errors":[{"message":"User not found"}],"data":null}	Yes	Handle error	Show error message: User not found
5	User retries query	N/A	N/A	Send query again	No output yet
6	Receive response	{"data":{"user":{"name":"Bob"}}}	No	Process data	Display user name: Bob

💡 Execution stops after successful data processing or after error handling and user decision.

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 6
response	null	{"data":{"user":{"name":"Alice"}}}	{"errors":[{"message":"User not found"}],"data":null}	{"data":{"user":{"name":"Bob"}}}
errorPresent	false	false	true	false
outputMessage	""	"Display user name: Alice"	"Show error message: User not found"	"Display user name: Bob"

Key Moments - 2 Insights

Why does the client check for errors even if data is present?

Because GraphQL responses can include both data and errors together, so the client must check the 'errors' field to know if something went wrong (see execution_table row 4).

What happens if the client ignores errors and processes data anyway?

The client might show incomplete or incorrect information, confusing users. The execution_table shows proper error handling at step 4 to avoid this.

Visual Quiz - 3 Questions

Look at the execution_table, what is the client output at step 2?

A Display user name: Alice

B Show error message: User not found

C No output yet

D Send query again

💡 Hint

Check the 'Output' column in execution_table row 2.

At which step does the client detect an error in the response?

A Step 2

B Step 6

C Step 4

D Step 1

💡 Hint

Look at the 'Error Present?' column in execution_table.

If the server always returns errors, how would the output column change?

A It would always show 'Display user name: ...'

B It would always show 'Show error message: ...'

C It would show 'No output yet' forever

D It would stop sending queries

💡 Hint

Refer to how errors are handled in execution_table rows 4 and 6.

Concept Snapshot

GraphQL client error handling:
- Send query and receive response
- Check if 'errors' field exists
- If errors, handle and show message
- Else, process and display data
- Optionally retry after errors

Full Transcript

In GraphQL client error handling, the client sends a query and waits for the server's response. Upon receiving the response, it checks if there is an 'errors' field. If no errors are present, the client processes and displays the data. If errors exist, the client handles them by showing an error message to the user. The user may retry the query, and the client repeats this process. This ensures users see correct information or clear error messages.