Verify if the transaction is present in rxjs

 private transactions = new BehaviorSubject([]);
  

   getTransactions(): Observable<ITransaction[]> {

     return this.transactions.asObservable();

  }

checkTransactionsExist():Observable<boolean>  {
   
  return this.getTransactions().pipe(map((results:any) =>  results.length > 0 ? true));
     
} // i need to verify if there is data in the transactions array

I encountered an issue, can you please help me rectify it?

https://i.stack.imgur.com/jODDm.png

ERROR:

  1. Argument of type 'unknown[]' is not assignable to parameter of type 'OperatorFunction<ITransaction[], boolean>'. Type 'unknown[]' provides no match for the signature '(source: Observable<ITransaction[]>): Observable'.

EDIT: I want to confirm if there are any transactions in the behavior subject array and return true if data exists or false otherwise

angulartypescriptionic-framework

Answer №1

In order to troubleshoot this issue, consider implementing the following steps. One key factor is adding types and updating the ternary statement, as it currently lacks an else condition. To simplify the return process, remember that results.length > 0 equates to 

results.length > 0 ? true : false
:

private transactions = new BehaviorSubject<ITransaction[]>([]);

getTransactions(): Observable<ITransaction[]> {
  return this.transactions.asObservable();
}

checkTransactionsExist():Observable<boolean>  {
  return this.getTransactions().pipe(map((results:ITransaction[]) => results.length > 0));   
}

Answer №2

Let's address the initial mistake:

Error: Expecting ':' at line 1005

The syntax results.length > 0 ? true is incorrect because ternary expressions require both the "if" and "else" parts (e.g. : something).

If you are seeking a boolean value of true or false, then results.length > 0 already provides that:

return this.getTransactions().pipe(map((results: any) => results.length > 0));

Keep in mind that using !!results.length will also generate a boolean result, achieving the same outcome as results.length > 0 (as results.length won't be negative and 0 can be interpreted as false). Refer to this source for performance insights.

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