Claude, 14. Februar 2016, 19:36 Uhr
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Gestern habe ich einen Abend damit vertubelt, nach dem Fehler zu suchen, der durch falsche oder doppelte Verwendung von Indexvariablen in einer verschachtelten Schleife auftritt. Ist „i“ schon verwendet? Greife ich einfach so darauf zu und exponiere es im globalen Namensraum? Wie komme ich in der verschachtelten Schleife an die Schlüssel von Objekten, und warum geht es trotzdem nicht so, wie zwanzig offene Stackoverflowtabs mir das weismachen wollen? Fragen über Fragen.
Heute Abend habe ich in der gleichen Zeit die ganze JavaScript-Datei neu geschrieben, aus dem Ärmel geschüttelt, ohne gross über Variablen, Zugriffe und Namensräume nachzudenken.
Was war geschehen?
Ich erstelle eine Datei db.coffee neben der bestehenden db.js.
Dann führe ich diesen Befehl aus:
coffee --compile .
Der rennt rekursiv durch alle Verzeichnisse, sucht nach *.coffee Dateien und generiert neben diesen am richtigen Platz das JavaScript Äquivalent. Die bestehenden JS-Dateien werden davon nicht berührt. Ich bin nicht gezwungen, komplett auf eine neue Programmiersprache umzusteigen; stattdessen kann ich Schritt für Schritt, Datei für Datei so konvertieren.
Ist das nicht ultraphänomenial?
Aber um was geht es eigentlich? Welcher Zauber lässt mich so schnell und einfach so komplexes JavaScript schreiben?
Ganz einfach: CoffeeScript.
Die Schleife vom Vorabend ist geradezu pythonisch einfach:
for database in databases
for docid in database
if docid == text
return db.new_id() |
for database in databases
for docid in database
if docid == text
return db.new_id()
Das, was ich da in ein paar Dezisekunden hingeschludert habe, generiert mir jetzt den Code, der mir am Vorabend die Nerven geraubt hat:
var database, docid, i, j, k, len, len1, text;
for (j = 0, len = databases.length; j < len; j++) {
database = databases[j];
for (k = 0, len1 = database.length; k < len1; k++) {
docid = database[k];
if (docid === text) {
return db.new_id();
}
}
} |
var database, docid, i, j, k, len, len1, text;
for (j = 0, len = databases.length; j < len; j++) {
database = databases[j];
for (k = 0, len1 = database.length; k < len1; k++) {
docid = database[k];
if (docid === text) {
return db.new_id();
}
}
}
Ich muss mich nicht darum kümmern, ob j oder k oder x schon belegt sind. Überhaupt muss ich mich gar nicht darum kümmern. Alle Variablen werden automatisch generiert und lokal definiert.
Hier wird auch nichts langsamer, im Gegenteil: Die Anzahl der databases (databases.length) wird in einer Wegwerfvariable len gespeichert, weil die for-Schleife sonst bei jedem Durchlauf die Länge ausliest. Alles so Sachen, Optimierungen und Tricks, für die man vorher dicke Bücher konsultieren musste, die sind hier direkt eingearbeitet.
Eine extra Bibliothek, die im Browser läuft und alles langsamer macht, braucht’s ebensowenig, denn das Resultat ist immer natives, schnelles und robustes JavaScript.
Man beachte auch, wie der Vergleichsoperator == zu === umgewandelt wird. Semikolons und Geschweifte Klammern gehen mir am Arsch vorbei; dafür setzt CoffeeScript sie dort, wo man sie manchmal vergisst und stellt Funktionen ein return voran, so dass auch der strengste Linter nichts mehr daran aussetzen kann.
commas = [
'a'
wrongly: 'placed'
'comma'
fucks: 'up'
'internet'
'explorer'
6
] |
commas = [
'a'
wrongly: 'placed'
'comma'
fucks: 'up'
'internet'
'explorer'
6
]
Hat jemand Kommaregel gesagt?
commas = [
'a', {
wrongly: 'placed'
}, 'comma', {
fucks: 'up'
}, 'internet', 'explorer', 6
]; |
commas = [
'a', {
wrongly: 'placed'
}, 'comma', {
fucks: 'up'
}, 'internet', 'explorer', 6
];
Gefährliche Stellen wie in Python einfach einrücken und ein try voranstellen…
try
console.log 'do dangerous stuff...' |
try
console.log 'do dangerous stuff...'
try {
console.log('do dangerous stuff...');
} catch (undefined) {} |
try {
console.log('do dangerous stuff...');
} catch (undefined) {}
Und ja, jQuery kann der auch:
$(document).ready ->
console.log 'dom is ready.' |
$(document).ready ->
console.log 'dom is ready.'
$(document).ready(function() {
return console.log('dom is ready.');
}); |
$(document).ready(function() {
return console.log('dom is ready.');
});
Nichts geht kaputt. Man kann CoffeeScript benutzen, oder auch nicht. Das funktioniert alles nebeneinander; wie bei einem Minifizierer. Nur, dass sich bei CoffeeScript die Lesbarkeit und somit die Wartbarkeit deutlich erhöht.
Wunderbar.
http://coffeescript.org/
