{"id":4310,"date":"2020-10-30T23:26:56","date_gmt":"2020-10-30T22:26:56","guid":{"rendered":"https:\/\/webhosting.de\/?p=4310"},"modified":"2020-10-30T23:26:56","modified_gmt":"2020-10-30T22:26:56","slug":"javascript","status":"publish","type":"post","link":"https:\/\/webhosting.de\/sv\/javascript\/","title":{"rendered":"JavaScript"},"content":{"rendered":"<p>JavaScript \u00e4r en av de tre stora utmaningarna inom webbhotell: f\u00f6rutom <a href=\"https:\/\/webhosting.de\/sv\/html-hypertext-markup-language\/\">HTML<\/a> (sidstruktur) och CSS (presentation), det objektorienterade programmeringsspr\u00e5ket erbjuder dynamisering av inneh\u00e5llet. Men JavaScript kan inte bara anv\u00e4ndas i samband med siddesign. Serverbaserade program kan ocks\u00e5 styras med JavaScript.<\/p>\n<h2>Ursprunget till JavaScript<\/h2>\n<p>Trots namnet har JavaScript inte mycket med Java att g\u00f6ra. Ursprungligen skulle skriptspr\u00e5ket heta LiveScript och utvecklades av Netscape f\u00f6r att Netscape Navigator skulle kunna interagera med Java-applets (Java-klientprogram). Eftersom JavaScript \u00e4r en egenutvecklad programvara var det en konkurrensfaktor f\u00f6r f\u00f6retag som t.ex. <a href=\"https:\/\/webhosting.de\/sv\/emails-microsoft-werden-abgewiesen\/\">Microsoft<\/a> representerade. Dessa svarade p\u00e5 utvecklingen av JavaScript med egna l\u00f6sningar, t.ex. skriptspr\u00e5ket JScript. Med tiden har dock JavaScript etablerat sig som det prim\u00e4ra skriptspr\u00e5ket, som nu st\u00f6ds av alla webbl\u00e4sare, f\u00f6r klientsidan och (f\u00f6rutom f\u00f6r <a href=\"https:\/\/webhosting.de\/sv\/php\/\">php<\/a>) dynamisering p\u00e5 serversidan.<\/p>\n<h3>Dynamisering p\u00e5 klientsidan<\/h3>\n<p>Den mest anv\u00e4nda funktionen i JavaScript \u00e4r f\u00f6rmodligen m\u00f6jligheten till dynamisering p\u00e5 klientsidan. Klienten \u00e4r webbl\u00e4saren. Dynamisering p\u00e5 klientsidan inneb\u00e4r att det konkreta inneh\u00e5ll som visas p\u00e5 klienten manipuleras. HTML \u00e4r den statiska beskrivningen av en webbplats struktur, den s\u00e5 kallade Document Object Model (DOM). Medan CSS (Cascading Style Sheets) anv\u00e4nds f\u00f6r den separata utformningen av detta \"skelett\", ger JavaScript m\u00f6jlighet att flytta, ta bort eller l\u00e4gga till HTML-element.<\/p>\n<p>Denna DOM-manipulering (DOM-skript) kan anv\u00e4ndas p\u00e5 m\u00e5nga olika s\u00e4tt. Funktioner \u00e4r till en b\u00f6rjan bundna till vissa h\u00e4ndelser via s\u00e5 kallade h\u00e4ndelsegivare. Det kan handla om anv\u00e4ndarens klick, tider eller till och med laddningen av webbplatsen. H\u00e4ndelsebaserade \u00e4ndringar kan sedan utl\u00f6sas via de ID:er som tilldelats element i HTML. Det kan handla om allt fr\u00e5n att programmera enkla, dynamiska formul\u00e4r eller tabellfilter till att b\u00e4dda in videospelare eller komplex, dynamisk grafik.<\/p>\n<h3>JQuery: Det mindre komplicerade JavaScript<\/h3>\n<p>JavaScript \u00e4r ett exempel p\u00e5 objektorienterade programmeringsspr\u00e5k. D\u00e4rf\u00f6r \u00e4r tr\u00f6skeln f\u00f6r oerfarna webbdesigners relativt h\u00f6g. JavaScript-biblioteket JQuery erbjuder en f\u00f6renklad syntax som m\u00f6jligg\u00f6r de vanligaste anv\u00e4ndningsomr\u00e5dena p\u00e5 ett snabbt och enkelt s\u00e4tt, utan att begr\u00e4nsa JavaScript-funktionerna (mycket). Medan JavaScript, med sin definition av prototyper (i st\u00e4llet f\u00f6r klasser), instanser (konkreta objekt) och metoder (funktioner som \u00e4r bundna till objekt), erbjuder en liknande komplexitet och \u00e4ndringsbarhet som till exempel Java eller Python, begr\u00e4nsar JQuery vokabul\u00e4ret och strukturerna. Kommandona \u00e4r n\u00e4stlingsbara, s\u00e5 strukturen kan f\u00f6rst\u00e5s ganska snabbt. Om det inte r\u00f6r sig om komplexa, ovanliga till\u00e4mpningar finns det d\u00e4rf\u00f6r med stor sannolikhet en enkel l\u00f6sning i JQuery.<\/p>\n<h3>Dynamisering p\u00e5 serversidan: AJAX och Node.js<\/h3>\n<p>F\u00f6rutom DOM-manipulering anv\u00e4nds JavaScript \u00e4ven f\u00f6r kommunikation med servrar, t.ex. f\u00f6r databasfr\u00e5gor. Sedan 2009 finns node.js, ett ramverk f\u00f6r dynamisering p\u00e5 serversidan med JavaScript. Detta var m\u00f6jligt redan f\u00f6re 2009, men node.js g\u00f6r det l\u00e4ttare att integrera. Detta \u00e4r en f\u00f6rdel f\u00f6r JavaScript-programmerare, eftersom de inte l\u00e4ngre beh\u00f6ver anv\u00e4nda andra spr\u00e5k som php. Dessutom m\u00f6jligg\u00f6r node.js parallellisering av processer. Detta \u00e4r en f\u00f6rdel eftersom f\u00f6r m\u00e5nga av dessa s\u00e5 kallade tr\u00e5dar kan leda till stillast\u00e5ende. Med node.js k\u00f6rs f\u00f6rfr\u00e5gningar p\u00e5 en enda tr\u00e5d, vilket kan \u00f6ka prestandan avsev\u00e4rt.<\/p>\n<p>Node.js \u00e4r ett exempel p\u00e5 m\u00f6jligheterna med AJAX. Akronymen st\u00e5r f\u00f6r ett f\u00f6rfarande som kallas Asynchronous JavaScript and XML. Denna princip g\u00f6r det m\u00f6jligt att beg\u00e4ra inneh\u00e5ll fr\u00e5n servrar utan att beh\u00f6va ladda om hela sidan. F\u00f6r m\u00e5nga webbtj\u00e4nster, t.ex. YouTube, skulle det vara en stor nackdel att beh\u00f6va ladda om helt och h\u00e5llet efter videof\u00f6rfr\u00e5gningar eller kommentarer. AJAX \u00e4r ocks\u00e5 en l\u00f6sning p\u00e5 problemet med ackumulerade f\u00f6rfr\u00e5gningar tack vare asynkron behandling, vilket f\u00f6rklaras ovan f\u00f6r Node.js.<\/p>\n<h3>Integrering av JavaScript<\/h3>\n<p>Den grundl\u00e4ggande integreringen av JavaScript i webbutbud fungerar p\u00e5 exakt samma s\u00e4tt som anslutningen till CSS-filer. Det finns tv\u00e5 m\u00f6jligheter till detta: JavaScript kan \u00e5 ena sidan anv\u00e4ndas i huvudet och \u00e5 andra sidan i kroppen av HTML-dokumentet.<\/p>\n<p>&nbsp;<\/p>","protected":false},"excerpt":{"rendered":"<p>JavaScript geh\u00f6rt zu den gro\u00dfen drei des Webhostings: Neben HTML (Seitenstruktur) und CSS (Darstellung) bietet die objektorientierte Programmiersprache Dynamisierung von Inhalten. Aber JavaScript ist nicht nur im Kontext der Seitengestaltung einsetzbar. Auch serverseitige Anwendungen k\u00f6nnen mit JavaScript kontrolliert werden. Urspr\u00fcnge von JavaScript Trotz des Namens hat JavaScript nur wenig mit Java zu tun. Urspr\u00fcnglich sollte 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