How to Ensure a Unique Email, userName will Enter into MongoDB using Mongoose

db.UserSchema = new db.Schema({   
    userName: {type:String,
        unique:true,
        required:true,index:true},
    emailId: {type:String,
        unique:true,
        required:true,index:true},
    password: {type:String,
        required:true},
    contactNumber: String,
    region: String,
    isActive:Boolean,
    lastLoginDateTime:Date
});

Above is the schema I would like to put into MongoDB, but email and userName should be unique and I am unable to do that.