nodejs error handling

  • error vs. exception
    • An error is any instance of the Error class. Errors may be constructed and then passed directly to another function or thrown.
    • When you throw an error, it becomes an exception.2Here’s an example of using an error as an exception:
      throw new Error('something bad happened');

      but you can just as well use an Error without throwing it:

      callback(new Error('something bad happened'));
    • and this is much more common in Node because most errors are asynchronous
  • try/catch
    • the only commonly-used case where you’d use try/catch is JSON.parse and other user-input validation functions
  • operational error vs. program error
    • operational error
      • run-time problems experienced by correctly-written programs. These are not bugs in the program. In fact, these are usually problems with something else: the system itself (e.g., out of memory or too many open files), the system’s configuration (e.g., no route to a remote host), the network (e.g., socket hang-up), or a remote service (e.g., a 500 error, failure to connect, or the like). Examples include:
        • failed to connect to server
        • failed to resolve hostname
        • invalid user input
        • request timeout
        • server returned a 500 response
        • socket hang-up
        • system is out of memory
    • program error
      • bugs in the program. These are things that can always be avoided by changing the code
    • failure to handle an operational error is itself a programmer error.
      • For example, if a program tries to connect to a server but it gets an ECONNREFUSED error, and it hasn’t registered a handler for the socket’s 'error' event, then the program will crash, and that’s a programmer error
    • The distinction between operational errors and programmer errors is the foundation for figuring out how to deliver errors and how to handle them
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