Error handling in JavaScript

Handle with careFehlerbehandlung in JavaScript

Friday 8 November 13

WER BIN ICH?

• Sebastian Springer

• https://github.com/sspringer82

• @basti_springer

Was ist ein Fehler?

☠Friday 8 November 13

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');}

} catch (RangeError e) { }

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

Callbacks

Fehler in CallbacksApplikation Asynchrone

Ausführung

Operation

Ausführung

Operation

Ausführung

Operation

☠☂ ☏☣☢

Ausführung

Operation

Callback☠☂ ☏☣☢

Ausführung

Operation

Callback☠☂ ☏☣☢

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

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

☠Friday 8 November 13

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) { ...});

Fehler in Callbacks

Error { errno: ... code: ... path: ... message: ...}

Events

Error EventsSubject Observer

Error Events

on(‘error’, function...

Subject Observer

Error Events

☠☂ ☏☣☢

Subject Observer

Error Events

☠☂ ☏☣☢

trigger(‘error’, {...

Subject Observer

Error Events

☠☂ ☏☣☢

trigger(‘error’, {...

Subject Observer

Promiseshttp://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) { ...});

Promisesfunction 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/qClient + Server

• https://github.com/kriszyp/node-promiseServer only

Node.js Domain

Node domain

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

domain.run(function () { ...});

Node Domain

• error-Events

• Exceptions

Wird ausgeführt bei:

window.onerror

catch it all!

window.onerror

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

window.onerror

und jetzt?

Logging FTW!

Logging

Client Server

Logging

Client

☠☂ ☏☣☢

Server

Logging

Client

☠☂ ☏☣☢

ServerLog Message

Logging

Client

☠☂ ☏☣☢

ServerLog Message

Loggingwindow.onerror = function (msg, url, nr){ $.ajax({ url: ‘/logger’ data: { msg: msg, url: url, nr: nr } }); return true;}Friday 8 November 13

Logging

Fire and Forget

Fragen?

Sebastian Springersebastian.springer@mayflower.de

Mayflower GmbHMannhardtstr. 680538 MünchenDeutschland

@basti_springer

https://github.com/sspringer82

Error handling in JavaScript

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