resolvers.js

const resolvers = {

  Mutation:{
        createNewUser(parent,args,ctx,info){
           const isEmailExists = users.some((user) => user.email === args.email)
           if(isEmailExists){
             throw new Error('Email already Taken')
           }

           const user = {
               id:uuidv4(),
               name:args.name,
               email:args.email,
               age:args.age
           }
           users.push(user)

           return user
        }
  }