Error handling in JavaScript

Handle with care
Fehlerbehandlung in JavaScript

Friday 8 November 13

WER BIN ICH?

•

Sebastian Springer

•

https://github.com/sspringer82

•

@basti_springer


Was ist ein Fehler?

☠

Was ist ein Fehler?

☠
Whoops, this should not happen.

Fehlertypen


Eigene Fehler

throw new Error('An error occurred');


Eigene Fehler
var MyErr = function (message) {
this.message = message;
this.name = 'MyErr';
}
MyErr.prototype = new Error();
MyErr.prototype.constructor = MyErr;


Abfangen von Fehlern
try {
throw new Error('Hello World');
} catch (e) {
console.log(e);
} finally {
console.log('Finished');
}


try {
} catch (RangeError e) {
}


try {
} catch (e) {
if (e instanceof RangeError) {
}
}


Callbacks


Fehler in Callbacks
Applikation


Asynchrone
Ausführung

Fehler in Callbacks
Asynchrone
Ausführung

Applikation
Operation


Fehler in Callbacks
Asynchrone
Ausführung

Applikation
Operation

☠☂ ☏☣☢


Fehler in Callbacks
Asynchrone
Ausführung

Applikation
Operation

Callback


☠☂ ☏☣☢

Fehler in Callbacks
function myTimeout() {
throw new Error("whoops");
}


Fehler in Callbacks
}
try {
setTimeout("myTimeout()", 0);
} catch (e) {
console.log(e);
}

Fehler in Callbacks

☠

}
try {
setTimeout("myTimeout()", 0);
} catch (e) {
console.log(e);
}

Fehler in Callbacks
$.ajax({
url: ‘/something’,
success: function (data) {
...
},
error: function (data) {
...
}
});


Fehler in Callbacks
var fs = require('fs');
fs.readFile('file', function (err, d) {
...
});


Fehler in Callbacks
var fs = require('fs');
fs.readFile('file', function (err, d) {
...
});
null


Fehler in Callbacks
Error {
errno: ...
code: ...
path: ...
message: ...
}


Error Events
Subject


Observer

Error Events
Subject

Observer
on(‘error’, function...


Error Events
Subject

Observer

☠☂ ☏☣☢


Error Events
Subject

Observer

☠☂ ☏☣☢

trigger(‘error’, {...


Promises
http://wiki.commonjs.org/wiki/Promises


Promises
In Javascript, promises are objects which represent the pending result of
an asynchronous operation.
(Martin Fowler)


Promises
$.ajax({
url: ‘/my/url’
}).done(function (data) {
...
}).fail(function (data) {
...
}).always(function (data) {
...
});


Promises
function promisedFunc() {
var def = $.Deferred();
// do something asynchronous
// success
def.resolve();
// fail
def.reject();
return def.promise();
}


Promises
promisedFunc().done(function () {
// success
}).fail(function () {
// failure
}).always(function () {
// success & failure
});


Promises
$.when(
promisedFunc(),
promisedFunc()
).then(success, failure);


Promises
•

http://api.jquery.com/category/deferred-object/
Client only

•

https://github.com/kriskowal/q
Client + Server

•

https://github.com/kriszyp/node-promise
Server only


Node.js Domain


Node domain
var domain = require(‘domain’).create();
domain.on(‘error’, function (err) {
console.log(err);
});
domain.run(function () {
...
});


Node Domain
Wird ausgeführt bei:

•
•


error-Events
Exceptions

window.onerror


window.onerror
catch it all!


window.onerror
window.onerror = function (msg, url, nr)
{
...
return true;
}


window.onerror
window.onerror

Code


und jetzt?


und jetzt?
Logging FTW!


Logging

Client


Server

Logging

Client

Server
☠☂ ☏☣☢


Logging

Log Message

Client
☠☂ ☏☣☢


Server

Logging
window.onerror = function (msg, url, nr)
{
$.ajax({
url: ‘/logger’
data: {
msg: msg,
url: url,
nr: nr
}
});
return true;
}

Logging
Fire and Forget


Sebastian Springer
sebastian.springer@mayflower.de
Mayflower GmbH
Mannhardtstr. 6
80538 München
Deutschland
@basti_springer
https://github.com/sspringer82


Error handling in JavaScript

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