medium tutorial token validation directive

index.js

const {SchemaDirectiveVisitor}  = require('graphql-tools')
const {defaultFieldResolver}  = require('graphql')
//...
class AuthDirective extends SchemaDirectiveVisitor {
    visitFieldDefinition(field) {
        const {resolve = defaultFieldResolver} = field
        const {roles: expectedRoles = []} = this.args
        console.log(expectedRoles.length);

        field.resolve = (...args) => {
          console.log(expectedRoles.length);
            const [, , context] = args
            if (context.jwt) {
                if (expectedRoles.length <= 0 ||
                    expectedRoles.some(r => context.jwt.roles.includes(r))
                ) {
                // Call original resolver if role check has passed
                  return resolve.apply(this, args)
                }
            }
            // We has two options here. throw an error or return null (if field is nullable).
            throw new Error(
                `You are not authorized. Expected roles: ${expectedRoles.join(', ')} for field ${field.name}`,
            )
        }
    }
}