FAQ: Learn JavaScript: Error Handling - The throw Keyword

This community-built FAQ covers the “The throw Keyword” exercise from the lesson “Learn JavaScript: Error Handling”.

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Web Development

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I’m wondering any difference between creating an Error object with and without the new keyword?

When I do throw Error('some error msg') and throw new Error('some error msg'), it seems to me that both are working exactly the same!

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What are some real-life situations in which a programmer would like to throw an error and halt the program? It seems to me that it would be better to indicate what’s wrong and give a chance for the user to fix it. :face_with_monocle:

And how would you “indicate what’s wrong and give a chance for the user to fix it”?

try {
  throw Error('some error msg');
} catch (error) {
  console.log(error.stack); // This might not work as expected, might be undefined

try {
  throw new Error('some error msg');
} catch (error) {
  console.log(error.stack); // This should provide the call stack

In the first case, where Error is called without new, accessing error.stack might not provide the call stack information. JavaScript implicitly creates an Error object with the given message, but it doesn’t allow you to customize it further or access properties like stack (the call stack at the time the error was thrown). This method is often considered a shorthand and may not provide as much information when debugging.

However, in the second case, where new Error is used, error.stack should work correctly and provide the call stack information. You’re explicitly constructing a new instance of the Error object, which gives you the ability to customize it further and access properties/methods available in Error objects, such as stack , message , name , etc. This allows for more detailed error handling and debugging capabilities.

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Just to name a few…

  1. Critical Errors: Some errors are so severe that continuing the program execution would lead to unpredictable or dangerous behavior. For example, if a function receives unexpected input that could compromise the security of the system, it might be appropriate to halt the program by throwing an error.
  2. Invariant Violations: Invariants are conditions that must always be true during the execution of a program. If an operation violates an invariant, it indicates a fundamental problem with the program’s logic or data integrity. Throwing an error in such cases helps to identify and fix these issues early.
  3. Missing Dependencies : If a program relies on external dependencies or resources that are not available or properly configured, it may not be able to continue execution safely. In such cases, throwing an error helps to communicate the problem and prevents potential data corruption or security vulnerabilities.
1 Like