The 'Promise<void>' type cannot be assigned to the 'Promise<xxx>' type

Question

The 'Promise<void>' type cannot be assigned to the 'Promise<xxx>' type

Attempting the following transaction in TypeScript resulted in a compile error. The error message stated:

Type 'Promise<void>' is not assignable to type 'Promise<transactionArgument>'

. However, the function returns a value of type transaction, which is of type transactionArgument.

I am puzzled by this issue and would greatly appreciate any insights or opinions on why it occurred.

type RegisterPricingTransactionInfo = (pricingTransaction:transactionArgument,createdAt:Date,createdBy:string,datasource:any) => Promise<transactionArgument>

export const  registerPricingTransactionInfo: RegisterPricingTransactionInfo = async (pricingTransaction,createdAt,createdBy,datasource) => {
    let urlCode;
    let transaction:transactionArgument;
    transaction = {test:"test"}

     await datasource.manager.transaction(async (transactionalEntityManager:EntityManager) =>{
     try {
        await transactionalEntityManager.save(transaction)
        return transaction;
     } catch (error) {
        console.error(error)
     }
    })
}

    "message": "Type '(pricingTransaction: transactionArgument, createdAt: Date, createdBy: string, datasource: any) => Promise<void>' is not assignable to type 'RegisterPricingTransactionInfo'.\n  Type 'Promise<void>' is not assignable to type 'Promise<transactionArgument>'.\n    Type 'void' is not assignable to type 'transactionArgument'."

Thank you for your help.

typescript typeorm

Answer 1

Answer №1

You are dealing with a situation where you have a nested callback. The inner callback is properly returning data, but the outer parent function is not.

One possible solution to identify the issue could be to ensure proper code indentation. This can help in spotting the problem more easily:

const recordPricingTransaction: RecordPricingTransaction = async (pricingTransaction, createdAt, createdBy, datasource) => {
  let urlCode;
  let transaction: transactionArgument;
  transaction = { test: "test" }

  await datasource.manager.transaction(async (transactionalEntityManager: EntityManager) => {
    try {
      await transactionalEntityManager.save(transaction)
      return transaction; // this return statement is within the nested callback
    } catch (error) {
      console.error(error)
    });
    // no return statement outside the nested callback?
}

Answer 2

You are dealing with a situation where you have a nested callback. The inner callback is properly returning data, but the outer parent function is not.

One possible solution to identify the issue could be to ensure proper code indentation. This can help in spotting the problem more easily:

const recordPricingTransaction: RecordPricingTransaction = async (pricingTransaction, createdAt, createdBy, datasource) => {
  let urlCode;
  let transaction: transactionArgument;
  transaction = { test: "test" }

  await datasource.manager.transaction(async (transactionalEntityManager: EntityManager) => {
    try {
      await transactionalEntityManager.save(transaction)
      return transaction; // this return statement is within the nested callback
    } catch (error) {
      console.error(error)
    });
    // no return statement outside the nested callback?
}

The 'Promise<void>' type cannot be assigned to the 'Promise<xxx>' type

Answer №1

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