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.

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"
            }
          }
        }
      ]
    }
  }
}