Reject a JavaScript Promise in a try-catch block [Tech Interview Quiz]

Last updated Jan 5, 2023

• JS Interview Quiz
• JavaScript

Promises are a useful tool in JavaScript for managing asynchronous tasks and handling errors.

When a promise is rejected, it enters a “rejected” state and triggers a rejection handler, which allows you to handle the error.

In tech interviews, you’ll be frequently asked to explore the different ways to handle promise rejection in JavaScript as incorrect handling of rejected promises leads to bugs and crashes.

Consider the code snippet and detemine how the program would behave.

Code snippet as a picture

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try {
  Promise.reject('an error occurred');
} catch (e) {
  console.log('the error was caught!');
}

What happens if you try to reject the promise inside of the JavaScript try/catch block. Will the error be caught in the catch block?

Explanation

Regular try/catch blocks only catch errors that appear in the synchronous code.

As the Promise in the second line doesn’t have its own asynchronous .catch block, the rejection will be left unhandled.

An UnhandledPromiseRejectionWarning will be raised and the code inside of the regular catch block will not be executed.

Answer

The error will not be caught and the message the error was caught! will NOT be logged to the console.