JavaScript je dynamick\u00fd, prototypov\u00fd, v\u00edceparadigmatick\u00fd<\/strong> programovac\u00ed jazyk, kter\u00fd b\u011b\u017e\u00ed v prohl\u00ed\u017ee\u010di i na serveru. Vznikl pro interaktivitu webu, dnes poh\u00e1n\u00ed front-end, back-end, mobiln\u00ed a desktopov\u00e9 aplikace<\/em>, skripty CI\/CD, automatizaci i edge computing<\/em>. Standardizov\u00e1n je jako ECMAScript (ES)<\/strong>; ka\u017edoro\u010dn\u00ed specifikace definuje jazykov\u00e9 konstrukce, kter\u00e9 implementuj\u00ed enginy (V8, SpiderMonkey, JavaScriptCore, Chakra\/Node-Chakra d\u0159\u00edve).<\/p>\n JavaScript pou\u017e\u00edv\u00e1 prototypy<\/strong>: ka\u017ed\u00fd objekt m\u00e1 intern\u00ed odkaz na \u201eprototyp\u201c (\u0159et\u011bzec prototyp\u016f). \u201eT\u0159\u00eddy\u201c ( JavaScript je single-threaded<\/strong> s event loopem. I\/O a \u010dasova\u010de b\u011b\u017e\u00ed mimo hlavn\u00ed vl\u00e1kno a zp\u011bt pl\u00e1nuj\u00ed \u00falohy pomoc\u00ed task<\/em> a microtask<\/em> front (microtasky \u2013 nap\u0159. vy\u0159\u00edzen\u00ed TypeScript p\u0159in\u00e1\u0161\u00ed struktur\u00e1ln\u00ed typov\u00e1n\u00ed<\/strong>, kter\u00e9 pom\u00e1h\u00e1 s \u00fadr\u017ebou velk\u00fdch k\u00f3dov\u00fdch z\u00e1kladen. V \u010dist\u00e9m JS lze pou\u017e\u00edt JSDoc<\/em> anotace a checkJs<\/em> pro postupn\u00e9 typov\u00e1n\u00ed. D\u016fle\u017eit\u00e9 je dr\u017eet hranici typ\u016f<\/strong> na vstupu a v\u00fdstupu modul\u016f (nap\u0159. generovat typy z API sch\u00e9mat).<\/p>\nJ\u00e1dro jazyka: hodnoty, typy a porovn\u00e1v\u00e1n\u00ed<\/h2>\n
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'2' * 3<\/code> \u2192 6<\/code>), kter\u00e9 mohou p\u0159ekvapit; pro porovn\u00e1n\u00ed preferujte ===<\/code> (striktn\u00ed shoda) p\u0159ed ==<\/code>.<\/li>\nNaN<\/code> je \u201enot a number\u201c a nen\u00ed rovno ni\u010demu, ani sob\u011b; testujte Number.isNaN()<\/code>.<\/li>\n<\/ul>\nPrototypov\u00e1 d\u011bdi\u010dnost a objektov\u00fd model<\/h2>\n
class<\/code>) jsou syntaktick\u00fd cukr nad prototypy. Metody jako Object.create()<\/code> nebo Object.setPrototypeOf()<\/code> d\u00e1vaj\u00ed jemnou kontrolu nad d\u011bdi\u010dnost\u00ed a slo\u017een\u00edm chov\u00e1n\u00ed.<\/p>\nRozsahy, uz\u00e1v\u011bry (closures) a this-binding<\/h2>\n
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let<\/code> a const<\/code> jsou blokov\u011b omezen\u00e9; var<\/code> je funk\u010dn\u011b omezen\u00fd a hoistuje se \u2013 pou\u017e\u00edvejte modern\u00ed deklarace.<\/li>\nthis<\/code>:<\/strong> hodnota se odv\u00edj\u00ed od zp\u016fsobu vol\u00e1n\u00ed. \u0160ipkov\u00e9 funkce (=><\/code>) nev\u00e1\u017eou<\/em> vlastn\u00ed this<\/code> (d\u011bd\u00ed lexik\u00e1ln\u011b), klasick\u00e9 funkce ano; pro kontrolu pou\u017eijte call<\/code>\/apply<\/code>\/bind<\/code>.<\/li>\n<\/ul>\nAsynchronn\u00ed model: event loop, Promise a async\/await<\/h2>\n
Promise<\/code> \u2013 maj\u00ed prioritu). async\/await<\/code> stav\u00ed na Promise a zp\u0159ehled\u0148uje asynchronn\u00ed k\u00f3d; nezapome\u0148te na try\/catch<\/code> a paralelizaci pomoc\u00ed Promise.all()<\/code>.<\/p>\nModuly: ES Modules (ESM) vs. CommonJS<\/h2>\n
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import<\/code>\/export<\/code>, statick\u00e1 anal\u00fdza, tree-shaking<\/em>, nativn\u00ed v prohl\u00ed\u017ee\u010d\u00edch i Node.js (s type=\"module\"<\/code> nebo p\u0159\u00edponou .mjs<\/code>).<\/li>\nrequire()<\/code>\/module.exports<\/code>, dynamick\u00e9 na\u010d\u00edt\u00e1n\u00ed, historicky v Node.js. V nov\u00fdch projektech preferujte ESM; interoperabilita vy\u017eaduje pozornost.<\/li>\n<\/ul>\nStandardn\u00ed knihovna a u\u017eite\u010dn\u00e9 struktury<\/h2>\n
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Map\/Set<\/code> (deterministick\u00e1 iterace, \u017e\u00e1dn\u00e9 kolize kl\u00ed\u010d\u016f jako u prost\u00fdch objekt\u016f), WeakMap\/WeakSet<\/code> pro cache s garbage-collection.<\/li>\nSymbol.iterator<\/code>; gener\u00e1tory (function*<\/code>) pro lazy sekvence a kontrolovan\u00e9 iterace.<\/li>\nSymbol.toStringTag<\/code>).<\/li>\nJavaScript a web: DOM, ud\u00e1losti a Web API<\/h2>\n
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querySelector<\/code>), delegace ud\u00e1lost\u00ed, pasivn\u00ed poslucha\u010de pro scroll\/touch ({ passive: true }<\/code>).<\/li>\nfetch<\/code> s AbortController, Readable\/Writable<\/em> Streams pro pr\u00e1ci s velk\u00fdmi daty.<\/li>\nServer-side JavaScript: Node.js, Deno a Bun<\/h2>\n
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Test Runner<\/code> a fetch<\/code>.<\/li>\nbun install<\/code>), kompatibilita s Node API.<\/li>\n<\/ul>\nN\u00e1stroje, bal\u00ed\u010dkov\u00e1n\u00ed a build<\/h2>\n
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Bezpe\u010dnost: XSS, CSRF, supply chain<\/h2>\n
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textContent<\/code> m\u00edsto innerHTML<\/code> pro u\u017eivatelsk\u00e1 data.<\/li>\nnpm audit<\/code>, lockfile signing<\/em>), pinning verz\u00ed, minim\u00e1ln\u00ed sadu bal\u00ed\u010dk\u016f.<\/li>\neval<\/code>.<\/li>\n<\/ul>\nV\u00fdkon: m\u011b\u0159en\u00ed, profily a optimalizace<\/h2>\n
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Architektury front-endu: SPA, SSR, SSG, ISR a edge<\/h2>\n
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Ekosyst\u00e9m framework\u016f a knihoven<\/h2>\n
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TypeScript a typov\u00e1n\u00ed v JS sv\u011bt\u011b<\/h2>\n
Pr\u00e1ce s daty: JSON, bin\u00e1rn\u00ed form\u00e1ty a \u010das<\/h2>\n
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JSON.parse\/stringify<\/code>, pozor na bezpe\u010dnost (neserializovat funkce, validovat sch\u00e9maty \u2013 AJV<\/em>).<\/li>\nArrayBuffer<\/code>, TypedArray<\/code>, DataView<\/code>, URL.createObjectURL<\/em> pro blob zdroje.<\/li>\nDate<\/code> je limitovan\u00fd; pou\u017e\u00edvejte osv\u011bd\u010den\u00e9 knihovny nebo modern\u00ed API v b\u011bz\u00edch, kter\u00e9 ho podporuj\u00ed. Z\u00e1sadou je dr\u017eet UTC v dom\u00e9nov\u00e9 vrstv\u011b a form\u00e1tovat a\u017e na okraji.<\/li>\n<\/ul>\nAPI vrstvy a s\u00ed\u0165ov\u00e1 komunikace<\/h2>\n
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Pr\u016fmyslov\u00e9 vzory a idiomy<\/h2>\n
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{ ...obj }<\/code>, [...arr]<\/code>), funk\u010dn\u00ed aktualizace, vyh\u00fdbat se neviditeln\u00fdm side-effect\u016fm.<\/li>\nTestovatelnost a kvalita<\/h2>\n
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Observabilita a provoz<\/h2>\n
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\u010cast\u00e9 chyby a jak se jim vyhnout<\/h2>\n
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await<\/code>; zachytit chyby (.catch<\/code> \/ try\/catch<\/code>), vyvarovat se \u201efloating promises\u201c.<\/li>\nChecklist pro produk\u010dn\u00ed JavaScript<\/h2>\n
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