Error TS2339: The 'email' property is not found in the 'FindUserProps' type

Question

Error TS2339: The 'email' property is not found in the 'FindUserProps' type

interface FindUserEmailProps {
   readonly email: string
}

interface FindUserIdProps {
   readonly id: string
}

type FindUserProps = FindUserEmailProps | FindUserIdProps

export const findUserByEmail = async ({ email }: FindUserProps): Promise<IUser> => {
   const user = await User.findOne({ email })
   if (!user) {
      throw new Error('User not found')
   }
   return user
}

I am experiencing an issue with the TS2339 error stating that 'Property 'email' does not exist on type 'FindUserProps'. Can anyone help explain why this is happening?

typescript express types

Answer 1

Answer №1

The reason for this behavior is that FindUserProps can only be either FindUserEmailProps or FindUserIdProps, not both simultaneously (which would require both FindUserEmailProps & FindUserIdProps). Therefore, TypeScript needs an assertion to determine which type it is.

In order to extract the email property from a FindUserProps, you must create your own type guard function to help TypeScript identify whether it's a FindUserEmailProps or FindUserIdProps.

// Custom type guard to specify if an object is FindUserEmailProps
function isFindUserEmailProps(obj: FindUserProps): obj is FindUserEmailProps {
  return "email" in obj;
}

export const findUserByEmail = async (userProps: FindUserProps): Promise<IUser> => {
   // Ensure userProps is of type FindUserEmailProps
   if (!isFindUserEmailProps(userProps)) {
      // To simplify, consider changing the function to accept only FindUserEmailProps
      throw new Error("Invalid userProps to find by email");
   }
   const {email} = userProps;
   const user = await User.findOne({ email })
   if (!user) {
      throw new Error('User not found')
   }
   return user
}

Answer 2

The reason for this behavior is that FindUserProps can only be either FindUserEmailProps or FindUserIdProps, not both simultaneously (which would require both FindUserEmailProps & FindUserIdProps). Therefore, TypeScript needs an assertion to determine which type it is.

In order to extract the email property from a FindUserProps, you must create your own type guard function to help TypeScript identify whether it's a FindUserEmailProps or FindUserIdProps.

// Custom type guard to specify if an object is FindUserEmailProps
function isFindUserEmailProps(obj: FindUserProps): obj is FindUserEmailProps {
  return "email" in obj;
}

export const findUserByEmail = async (userProps: FindUserProps): Promise<IUser> => {
   // Ensure userProps is of type FindUserEmailProps
   if (!isFindUserEmailProps(userProps)) {
      // To simplify, consider changing the function to accept only FindUserEmailProps
      throw new Error("Invalid userProps to find by email");
   }
   const {email} = userProps;
   const user = await User.findOne({ email })
   if (!user) {
      throw new Error('User not found')
   }
   return user
}

Error TS2339: The 'email' property is not found in the 'FindUserProps' type

Answer №1

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