Graphql - How to get type (String, Int, ID etc..) of a selected field

Question

I have the following graphql query

const GET_USER = gql`
    query user() {
        user {
            firstName
            lastName
        }
    }
`

I traverse through the query to find the type of the firstName & the lastName field using visit function provided by graphql

visit(GET_USER, {
    Field(node) {
      console.log(node)
    }
  }

it looks like the fields contain only the following information.

{
      kind: 'Field',
      alias: undefined,
      name: { kind: 'Name', value: 'firstName' },
      arguments: [],
      directives: [],
      selectionSet: undefined
},
{
      kind: 'Field',
      alias: undefined,
      name: { kind: 'Name', value: 'lastName' },
      arguments: [],
      directives: [],
      selectionSet: undefined
}

which doesn't tell me the type of firstName & lastName

I am expecting that I will probably have to make use of the related schema file to get the types of that query but I am not sure how to do that, if anyone can help me with that, that would be great.

Answer 1

Use Introspection

Not sure what platform you're using but introspection is what you use to get information on a particular type.

Introspection is the ability to query which resources are available in the current API schema.

Example for User type:

{
  __type(name: "User") {
     name
     kind
  }
}

Example Response:

{
  "data": {
    "__type": {
      "name": "User",
      "kind": "OBJECT"
    }
  }
}

You can use introspection to drill into fields as well:

{
  __type(name: "User") {
    name
    fields {
      name
      type {
        name
        kind
      }
    }
  }
}

Example Response:

{
  "data": {
    "__type": {
      "name": "User",
      "fields": [
        {
          "name": "id",
          "type": {
            "name": null,
            "kind": "NON_NULL",
            "ofType": {
              "name": "ID",
              "kind": "SCALAR"
            }
          }
        },
        {
          "name": "name",
          "type": {
            "name": null,
            "kind": "NON_NULL",
            "ofType": {
              "name": "String",
              "kind": "SCALAR"
            }
          }
        }
      ]
    }
  }
}