Error.md

Error-handling guidelines

There is a difference between error and exception. Error is a normal result and regular application behaviour that should not break execution sequence while exception breaks execution sequence (serving client-side request or certain asynchronous business-logic scenario).

Return error from method

(async ({ ...args }) => {
  const data = await doSomething();
  if (domain.module.validate(data)) {
    return data;
  } else {
    return new Error('Data is not valid', 10);
  }
});

Result with data (metacom packet): {"callback":1,"result":{"key":"value"}}

Result with error (metacom packet): {"callback":1,"error":{"message":"Data is not valid","code":10}}

Raise exception

• Application server will return HTTP 500 or abstract RPC error code.
• Application server may transfer exceptions over the network without stack trace and sensitive error messages (all this data will be logged instead).

(async ({ ...args }) => {
  throw new Error('Method is not implemented');
});

Result with exception (metacom packet):
{"callback":1,"error":{"message":"Internal Server Error","code":500}}

How to override error codes:
throw new Error('Method is not implemented', 404);
This will take error message from code:
{"callback":1,"error":{"message":"Not found","code":404}}

If you specify unknown code like this:
throw new Error('Method is not implemented', 12345);
This will generate: "Internal Server Error" with "code":500