Render available data while surfacing execution errors
Client response handling
GraphQL · Class
GraphQLError
GraphQL reports problems in a response-level errors entry. Request errors stop execution and omit data, while field errors can be returned with partial data.
How it works
GraphQL represents raised problems in the response's errors entry. Request errors happen before execution and omit data, while field errors occur during execution and can coexist with partial data; each error includes a developer-facing message, and may include locations or a path.
Returns
A GraphQL response can include an errors entry containing error information; it may also include data for a partial response.
Key points
- GraphQL defines a standard response format for reporting errors rather than prescribing a language-specific exception class.
- Use each error's message as the primary developer-oriented description of what went wrong.
- A locations entry can point clients or tools to the relevant position in the submitted operation.
- Execution-time failures are field errors, such as a resolver throwing or returning an invalid value.
- A response may expose errors alongside data and optional implementation-specific extensions.
- Valid GraphQL responses include data, errors, or both; they are not empty response maps.
Common mistakes
- Syntax and validation failures prevent execution, so the response does not contain data.
- A field failure does not necessarily discard all results; clients should handle data and errors together.
Example: Handling a partial GraphQL response
const result = {
data: { user: null },
errors: [{
message: "User not found",
path: ["user"]
}]
};
if (result.errors) {
for (const error of result.errors) console.error(error.message);
}A client can inspect the errors array while still using any partial data returned by the operation.
When to use it
Use messages and locations to identify invalid operations
Query diagnostics
Record field failures reported during execution
Resolver monitoring
Interview questions
QWhat kinds of errors can appear in a GraphQL response?
GraphQL responses can contain data, errors, or both. Request errors occur before execution and therefore exclude data, while execution-time field errors may produce partial data alongside errors.
Follow-up: How should a client distinguish a malformed operation from a resolver failure? A missing data field indicates a request-stage problem; data together with errors indicates an execution-stage problem.
QWhat information does a GraphQL error provide?
The errors entry contains information about raised errors, and each error includes a message intended to help developers understand the problem. A location may identify where the issue occurred in the document.
Follow-up: What additional information can identify an execution failure? The path can indicate the response field where the failure occurred.
QCan a response contain both data and errors?
A GraphQL response must include at least one of data or errors. If execution produces a field error, GraphQL can continue resolving other fields and return a partial response.
Follow-up: What happens when a non-null field cannot produce a value? Nullability propagation can make a containing field, or larger portion of the response, null while the error remains reported.
Related
dataerrorsextensionsrequest errorsfield errorspartial responselocationspath