2013-06-15 - Software Craftsmanship mit JavaScript

Software Craftsmanship
bit.ly/jsCraftsmanship
Interaktive Version der Präsentation!
Created by Johannes Hoppe

JohannesHoppe.de
bit.ly/jsCraftsmanship
Interaktive Version der Präsentation!

PrinzipienWissen
Werkzeuge
Wiederholung

Implied globals
Forgetting var
var foo = function() {
bar = 1;
};

Boolean type conversion
To Truthy or to Falsy. That is the only question!
var el = document.getElementById('does_not_exist');
if(el == false) {
alert("shouldn't we see this message?!");
}

Trailing comma
works on my machine!
var foo = {
bar: "bar",
baz: "baz",
};

Return undefined
señor developers wear mustaches
{
return
{
x : "looks like C# now!"
};
}

Associative arrays
they don't exist
var x = [];
x['foo'] = "bar";

try .. catch .. finally
who cares about the reason?
try {
doCrazyStuff;
} catch (e) {
return false;
}
return true;
};

Hoisting
declare upfront all variables
var foo = "global";
var bar = function() {
alert(foo);
var foo = "local";
alert(foo);
};

Eval
... and the job is done
function poorMansJsonParser(text) {
return eval("(" + text + ")");
}
var text = ' { "hello" : "world" } ';
var json = poorMansJsonParser(text);

Eval is evil!
Never ever!
var text = ' function() { alert("hacked!"); })( ';

Globals
the mother of all antipatterns
function foo() {
return "bar";
}
console.log(this['foo']());

Every time you clutter the global namespace,
somewhere in the world a helpless kitten dies!

Globals
reduce, minimize, delete or kill them
(function() { "wtf?" })();

The switch-case
syndrome
a functional language wants functions!
switch (something) {
case 1:
doFirst();
break;
case 2:
doSecond();
break;
case 3:
doThird();
break;
}

Lookup tables
avoid the switch-case syndrome
var methods = {
1: doFirst,
2: doSecond,
3: doThird
};
if (methods[something]) {
methods[something]();
}

Revealing Module
Pattern
var myRevealingModule = function () {
var _name = "Johannes";
function greetings() {
console.log("Hello " + _name);
}
function setName(name) {
_name = name;
}
return {
setName: setName,
greetings: greetings
};
}();
» Documentation

Modul loaders
use AMD (require.js)
define('test', ['jquery'], function() {
return {
saySomething : function() { alert("hello!"); }
}
});
require(['test'], function(t) {
t.saySomething();
});

Events
Publish/Subscribe Pattern
var $events = $({});
$events.bind('somethingHappens', function() {
alert("Something happened!");
});
$events.trigger('somethingHappens');

Visual Studio 2010/2012
/ F12
JScript Editor Extensions
Resharper 7.1
JSHint
Chutzpah
Firebug

Why Jasmine?
BDD-style similar to JSpec or RSpec,
created by authors of jsUnit and Screw.Unit
independent from any browser, DOM,
framework or host language
integrates into continuous build systems

Jasmine Bootstrap
<!DOCTYPEhtml>
<html>
<head>
<title>JasmineSpecRunner</title>
<linkrel="stylesheet"href="lib/jasmine-1.3.1/jasmine.css"/>
<scriptsrc="lib/jasmine-1.3.1/jasmine.js"></script>
<scriptsrc="lib/jasmine-1.3.1/jasmine-html.js"></script>

<scriptsrc="src/Player.js"></script>
<scriptsrc="src/Song.js"></script>

<scriptsrc="spec/SpecHelper.js"></script>
<scriptsrc="spec/PlayerSpec.js"></script>
<script>
(function(){
varhtmlReporter=newjasmine.HtmlReporter();
varjasmineEnv=jasmine.getEnv();
jasmineEnv.addReporter(htmlReporter);
jasmineEnv.specFilter=function(spec){
returnhtmlReporter.specFilter(spec);
};
varcurrentWindowOnload=window.onload;
window.onload=function(){

Output
finished in 0.009s
•••••
No try/catch
Jasmine 1.3.1 revision 1354556913
Passing5specs
Player
should be able to play a Song
when song has been paused
should indicate that the song is currently paused
should be possible to resume
tells the current song if the user has made it a favorite
#resume
should throw an exception if song is already playing

Hello World
hint: press F12 and paste this code!
var helloWorld = function() {
return "Hello World!";
};
describe('helloWorld', function() {
it('says hello', function() {
expect(helloWorld()).toEqual("Hello World!");
});
});
jasmine.getEnv().execute();

If I would have had time...
“ ”

Learn TDD
Improve by self reflection
Improve by feedback of others
Help others to improve
Teach TDD
Learn a new language

Test-Driven Development
1. Write your tests
2. Watch them fail
3. Make them pass
4. Refactor
5. Repeat
see , page 6
see , page 62 or many other
Growing Object-Oriented Software, Guided by Tests
Working Effectively with Legacy Code

1. Write your test
describe("saveFormat", function () {
var original = '{0} - {1} - {2}';
it("should replace placeholders", function () {
var expected = 'A - B - C';
var formated = saveFormat(original, 'A', 'B', 'C');
expect(formated).toEqual(expected);
});
it("should encode injected content", function () {
var expected = 'A - <b>TEST</b> - C';
var formated = saveFormat(original, 'A', '<b>TEST</b>', 'C');
expect(formated).toEqual(expected);
});
});

2. Watch them fail
var saveFormat = function() {
return "boo!";
};
Demo

3. Make them pass
var saveFormat = function(txt) {
$(arguments).each(function (i, item) {
if (i > 0) {
item = ($('<div/>').text(item).html());
txt = txt.replace("{" + (i - 1) + "}", item);
}
});
return txt;
};
Demo

4. Refactor
function htmlEncode(input) {
return ($('<div/>').text(input).html());
}
var saveFormat = function(txt) {
$.each(arguments, function (i, item) {
if (i > 0) {
item = htmlEncode(item);
txt = txt.replace("{" + (i - 1) + "}", item);
}
});
return txt;
};
Demo

5. Repeat
function htmlEncode(input) {
return ($('<div/>').text(input).html());
}
var saveFormat = function() {
var args = Array.prototype.slice.call(arguments);
var txt = args.shift();
$.each(args, function (i, item) {
item = htmlEncode(item);
txt = txt.replace("{" + i + "}", item);
});
return txt;
};
Demo

Deep practice
http://codekata.pragprog.com/
http://katas.softwarecraftsmanship.org/

2013-06-15 - Software Craftsmanship mit JavaScript

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