Resolver function signature in GraphQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the correct resolver function signature

Which of the following is the correct signature for a GraphQL resolver function?

A function resolver(parent, args, context, info) { ... }

B function resolver(args, parent, context) { ... }

C function resolver(context, args, parent, info) { ... }

D function resolver(info, context, args, parent) { ... }

💡 Hint

Remember the order: parent, arguments, context, and info.

The standard resolver function signature in GraphQL is function resolver(parent, args, context, info). This order is important because GraphQL passes these parameters in this sequence.

❓ query_result

intermediate

Output of resolver accessing arguments

Given this resolver function, what will be the output if called with args = { id: 5 }? function resolver(parent, args, context, info) { return args.id * 2; }

GraphQL

function resolver(parent, args, context, info) {
  return args.id * 2;
}

A undefined

B 5

C NaN

D 10

💡 Hint

Look at how the argument 'id' is used inside the function.

The resolver multiplies the id argument by 2. Since id is 5, the output is 10.

📝 Syntax

advanced

Identify the syntax error in resolver function

Which option contains a syntax error in the resolver function signature?

A const resolver = (parent, args, context, info) => { return args.value; }

B function resolver(parent args, context, info) { return args.value; }

C function resolver(parent, args, context, info) { return args.value; }

D const resolver = function(parent, args, context, info) { return args.value; }

💡 Hint

Check the commas between parameters.

Option B is missing a comma between parent and args, causing a syntax error.

❓ optimization

advanced

Best practice for using context in resolver

Which option shows the best practice for accessing user information from context inside a resolver?

A function resolver(parent, args, context, info) { return parent.user.id; }

B function resolver(parent, args, context, info) { return args.user.id; }

C function resolver(parent, args, context, info) { return context.user.id; }

D function resolver(parent, args, context, info) { return info.user.id; }

💡 Hint

User info is usually stored in context, not args or parent.

Context is the place to store per-request data like authenticated user info. Accessing context.user.id is the best practice.

🔧 Debug

expert

Why does this resolver throw an error?

Consider this resolver: function resolver(parent, args, context, info) { return args.input.value; } If the query is called without the 'input' argument, what error will occur?

A TypeError: Cannot read property 'value' of undefined

B ReferenceError: input is not defined

C SyntaxError: Unexpected token

D No error, returns undefined

💡 Hint

What happens if you try to access a property of undefined?

If args.input is undefined, trying to access value on it causes a TypeError.