Question

In web app development I would like a consistent way to catch and report error conditions. For example, a database update routine may detect a variety of error conditions and ideally I would like the application to capture them and report gracefully. The code below din’t work because retdiag is undefined when error is thrown…

function saveData(app,e) {
var db ;
var retdiag = ""; 
var lock = LockService.getPublicLock();
lock.waitLock(30000);
try {
// e.parameters has all the data fields from form
// re obtain the data to be updated
db = databaseLib.getDb();
var result = db.query({table: 'serviceUser',"idx":e.parameter.id});
if (result.getSize() !== 1) {
throw ("DB error - service user " + e.parameter.id);
}
//should be  one & only one
retdiag = 'Save Data Finished Ok'; 
}
catch (ex) {

retdiag= ex.message  // undefined!
}
finally {
lock.releaseLock();
return retdiag;
}
}

Is there a good or best practice for this is GAS?

Answer 1

To have a full error object, with message and stacktrace you have to build one, and not just throw a string. e.g. throw new Error("DB error ...");

Now, a more “consistent” way I usually implement is to wrap all my client-side calls into a function that will treat any errors for me. e.g.

function wrapper_(f,args) {
  try {
    return f.apply(this,args);
  } catch(err) {
    ;//log error here or send an email to yourself, etc
    throw err.message || err; //re-throw the message, so the client-side knows an error happend
  }
}

//real client side called functions get wrapped like this (just examples)
function fileSelected(file,type) { return wrapper_(fileSelected_,[file,type]); }
function loadSettings(id) { return wrapper_(loadSettings_,[id]); }

function fileSelected_(file,type) {
  ; //do your thing
}

function loadSettings_(id) {
  ; //just examples
  throw new Error("DB error ...");
}