Function getErrorMessage

getErrorMessage(error: unknown): string

Reads a human-readable message from anything that can be thrown. A catch variable is typed unknown, so error.message doesn't type-check; this narrows it safely. Used to put the cause in a logger call's message (see the last example).

Parameters

error: unknown
Whatever was thrown or rejected with

Returns string

An Error's message (its name when the message is empty), a string as-is, or the string form of anything else; "Unknown error" if even that fails

Example

getErrorMessage(new TypeError('bad input')); // 'bad input'
getErrorMessage(new Error(''));              // 'Error'
getErrorMessage('user_aborted');             // 'user_aborted'
getErrorMessage({ code: 1 });                // '[object Object]'
getErrorMessage(undefined);                  // 'undefined'

// In a logger call, message first and the error itself in the object:
logger.warn(`Failed to load: ${getErrorMessage(error)}`, { error });

Source

export function getErrorMessage(error: unknown): string {
  if (error instanceof Error) {
    return error.message || error.name;
  }
  if (typeof error === 'string') {
    return error;
  }
  try {
    return String(error);
  } catch {
    // e.g. an object with a null prototype has no toString.
    return 'Unknown error';
  }
}