{"id":3502,"date":"2022-06-21T14:00:00","date_gmt":"2022-06-21T14:00:00","guid":{"rendered":"http:\/\/the-codest.localhost\/blog\/functional-programming-in-javascript-part-3-functor-monad-maybe\/"},"modified":"2026-03-11T05:59:01","modified_gmt":"2026-03-11T05:59:01","slug":"funkcionalni-programovani-v-javascriptu-3-cast-funktor-monada-mozna","status":"publish","type":"post","link":"https:\/\/thecodest.co\/cs\/blog\/functional-programming-in-javascript-part-3-functor-monad-maybe\/","title":{"rendered":"Funkcion\u00e1ln\u00ed programov\u00e1n\u00ed v JavaScript, \u010d\u00e1st 3 - Funktor a mon\u00e1da Mo\u017en\u00e1"},"content":{"rendered":"<h2 class=\"wp-block-heading\">\u00davod<\/h2>\n\n\n\n<p>\u010casto je obt\u00ed\u017en\u00e9 udr\u017eovat nemodifikovatelnost. Vzor zabalen\u00ed <a href=\"https:\/\/thecodest.co\/cs\/blog\/app-data-collection-security-risks-value-and-types-explored\/\">data<\/a> do kontejneru p\u0159ich\u00e1z\u00ed na pomoc. Zaji\u0161\u0165uje hodnoty tak, aby manipulace s nimi byla bezpe\u010dn\u00e1 s vylou\u010den\u00edm vedlej\u0161\u00edch \u00fa\u010dink\u016f.<\/p>\n\n\n\n<p>Pokud jste tu nov\u00ed, ur\u010dit\u011b si p\u0159e\u010dt\u011bte m\u00e9 posledn\u00ed dva d\u00edly t\u00fdkaj\u00edc\u00ed se funkcion\u00e1ln\u00edho programov\u00e1n\u00ed na str\u00e1nk\u00e1ch <a href=\"https:\/\/thecodest.co\/cs\/blog\/vibrant-upturn-charting-the-resolute-rise-of-swedish-firms\/\">The Codest<\/a> blog o:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><a href=\"https:\/\/thecodest.co\/blog\/power-of-functional-programming-in-javascript-part-1-introduction\">\u010c\u00e1st 1 - \u00davod<\/a><\/li>\n\n\n\n<li><a href=\"https:\/\/thecodest.co\/blog\/power-of-functional-programming-in-javascript-part-2-combinators\">\u010c\u00e1st 2 - Kombin\u00e1tory<\/a><\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Funktor<\/h2>\n\n\n\n<p>Nem\u00e1 \u017e\u00e1dnou slo\u017eitou logiku. Jeho hlavn\u00edm \u00fakolem je obalit kontext a prov\u00e1d\u011bt na n\u011bm funkce, kter\u00e9 obdr\u017e\u00ed zven\u010d\u00ed. P\u0159i ka\u017ed\u00e9 zm\u011bn\u011b hodnoty je p\u0159ebalena a vr\u00e1cena nov\u00e1 instance kontejneru. P\u0159i vol\u00e1n\u00ed <b>mapa<\/b> kter\u00e1 prov\u00e1d\u00ed ur\u010ditou akci, vrac\u00ed novou instanci kontejneru s hodnotou vr\u00e1cenou p\u0159edanou funkc\u00ed, p\u0159i\u010dem\u017e je zachov\u00e1n princip nemodifikovatelnosti.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Prohl\u00e1\u0161en\u00ed<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"javascript\" class=\"language-javascript\"><code> const Functor = value =&gt; ({ {\n     map: fn =&gt; Functor(fn(value)),\n     chain: fn =&gt; fn(value),\n     of: () =&gt; value\n });<\/code><\/code><\/pre>\n\n\n\n<p><b>mapa<\/b> - u\u017eite\u010dn\u00e9, kdy\u017e chcete zm\u011bnit stav hodnoty v kontejneru, ale je\u0161t\u011b ji nechcete vr\u00e1tit.<\/p>\n\n\n\n<p><b>\u0159et\u011bz<\/b> - se pou\u017e\u00edv\u00e1, pokud chcete funkci p\u0159edat hodnotu, ani\u017e byste zm\u011bnili stav kontejneru. Obvykle na konci <b>mapa<\/b> telefon\u00e1ty.<\/p>\n\n\n\n<p><b>z<\/b> - vr\u00e1tit aktu\u00e1ln\u00ed hodnotu<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Imperativn\u00ed p\u0159\u00edklad<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"javascript\" class=\"language-javascript\">const randomInt = (max) =&gt; Math.floor(Math.random() * (max + 1))\n\nconst randomNumber = randomInt(200) \/\/ vrac\u00ed \u010d\u00edslo mezi 0 a 200\n\ndecrease(randomNumber) \/\/ vrac\u00ed (\u010d\u00edslo mezi 0 a 200) - 1<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\">Deklarativn\u00ed p\u0159\u00edklad<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"javascript\" class=\"language-javascript\">const randomIntWrapper = (max) =&gt;\nFunctor(max)\n.map(increase) \/\/ max + 1\n.map(multiplyBy(Math.random())) \/\/ Math.random() * (max + 1)\n.map(Math.floor) \/\/ Math.floor(Math.random() * (max + 1))\n\nconst randomNumber = randomIntWrapper(200)\n\nrandomNumber.of() \/\/ vrac\u00ed \u010d\u00edslo mezi 0 a 200\nrandomNumber.chain(decrease) \/\/ vrac\u00ed (\u010d\u00edslo mezi 0 a 200) - 1<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">Mon\u00e1dy<\/h2>\n\n\n\n<p>N\u011bkdy je krom\u011b funkc\u00ed, kter\u00e9 spou\u0161t\u011bj\u00ed nov\u00fd stav hodnoty, pot\u0159eba dal\u0161\u00ed logika skryt\u00e1 v kontejneru. V tomto p\u0159\u00edpad\u011b se hod\u00ed mon\u00e1da, kter\u00e1 je roz\u0161\u00ed\u0159en\u00edm funkce <b>funktor<\/b>. M\u016f\u017ee nap\u0159\u00edklad rozhodnout, co se m\u00e1 st\u00e1t, kdy\u017e hodnota nab\u00fdv\u00e1 ur\u010dit\u00e9 hodnoty, nebo jakou cestou se maj\u00ed ub\u00edrat dal\u0161\u00ed akce.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Mon\u00e1da Mo\u017en\u00e1<\/h2>\n\n\n\n<p>Mon\u00e1dy mo\u017en\u00e1 \u0159e\u0161\u00ed probl\u00e9m hodnot, kter\u00e9 nevracej\u00ed true. Kdy\u017e se to stane, n\u00e1sledn\u00e9 <b>mapa<\/b> je ignorov\u00e1no, ale umo\u017e\u0148uje vr\u00e1tit alternativu vol\u00e1n\u00edm p\u0159\u00edkazu <b>getOr<\/b> metoda. Umo\u017e\u0148uje vyhnout se pou\u017eit\u00ed oper\u00e1tor\u016f if \/ else, kter\u00e9 jsou obl\u00edben\u00e9 v metod\u00e1ch typu <b>imperativ<\/b> programov\u00e1n\u00ed. Tato mon\u00e1da se skl\u00e1d\u00e1 ze t\u0159\u00ed kontejner\u016f:<\/p>\n\n\n\n<p><b>Nic<\/b> - se spust\u00ed, kdy\u017e do kontejneru spadne hodnota, kter\u00e1 nen\u00ed true nebo <strong>filtr<\/strong> metoda vrac\u00ed false. Pou\u017e\u00edv\u00e1 se k simulaci prov\u00e1d\u011bn\u00ed funkce. To znamen\u00e1, \u017ee tento kontejner p\u0159ijme funkci, ale neprovede ji.<\/p>\n\n\n\n<p><b>Jen<\/b> - je to hlavn\u00ed kontejner, kter\u00fd vykon\u00e1v\u00e1 v\u0161echny funkce, ale pokud se hodnota zm\u011bn\u00ed na hodnotu false nebo <b>filtr<\/b> se vr\u00e1t\u00ed false, p\u0159ed\u00e1 ji metod\u011b <b>Nic<\/b> kontejner.<\/p>\n\n\n\n<p><b>Mo\u017en\u00e1<\/b> - Vezmu po\u010d\u00e1te\u010dn\u00ed hodnotu a rozhodnu se, jak\u00fd kontejner zavolat na za\u010d\u00e1tku.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Prohl\u00e1\u0161en\u00ed<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"javascript\" class=\"language-javascript\">const Just = value =&gt; ({\nmap: fn =&gt; Maybe(fn(value)),\nchain: fn =&gt; fn(value),\nof: () =&gt; value,\ngetOr: () =&gt; value,\nfilter: fn =&gt; fn(value) ? Just(value) : Nic(),\ntype: 'just'\n});\n\nconst Nothing = () =&gt; ({\nmap: fn =&gt; Nothing(),\nchain: fn =&gt; fn(),\nof: () =&gt; Nothing(),\ngetOr: substitute =&gt; substitute,\nfilter: () =&gt; Nothing(),\ntype: \"nothing\n});\n\nconst Maybe = value =&gt;\nvalue === null || value === undefined || value.type === 'nothing'\n? nic()\n: Just(value)<\/code><\/pre>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"\/app\/uploads\/2024\/05\/table.png\" alt=\"metody tabulky funktor \" title=\"tabulkov\u00fd funktor \"\/><\/figure>\n\n\n\n<p>Nyn\u00ed nav\u00e1\u017eeme na p\u0159edchoz\u00ed p\u0159\u00edklad o podm\u00ednce. Pokud je max v\u011bt\u0161\u00ed ne\u017e nula, funkce se provede. V opa\u010dn\u00e9m p\u0159\u00edpad\u011b vr\u00e1t\u00ed 0.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Imperativn\u00ed p\u0159\u00edklad<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"javascript\" class=\"language-javascript\">const randomInt = (max) =&gt; {\nif(max &gt; 0) {\nreturn Math.floor(Math.random() * (max + 1))\n} else {\nreturn 0\n}\n}\n\nconst bookMiddlePage = 200\n\nconst randomPage = randomInt(10) || bookMiddlePage \/\/ vrac\u00ed n\u00e1hodnou hodnotu\nconst randomPage = randomInt(-10) || bookMiddlePage \/\/ vrac\u00ed 200<\/code><\/pre>\n\n\n\n<h3 class=\"wp-block-heading\">Deklarativn\u00ed p\u0159\u00edklad<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"javascript\" class=\"language-javascript\">const randomIntWrapper = (max) =&gt;\nMaybe(max)\n.filter(max =&gt; max &gt; 0) \/\/ hodnota false ignoruje dal\u0161\u00ed vol\u00e1n\u00ed\n.map(increase)\n.map(multiplyBy(Math.random()))\n.map(Math.floor)\n\nconst bookMiddlePage = 200\n\n\/\/ Jen kontejner\nconst randomPage = randomIntWrapper(10).getOr(bookMiddlePage) \/\/ vrac\u00ed n\u00e1hodn\u00fd \u00fadaj\n\/\/ Nic kontejneru\nconst randomPage = randomIntWrapper(-10).getOr(bookMiddlePage) \/\/ vrac\u00ed 200<\/code><\/pre>\n\n\n\n<p><br><a href=\"https:\/\/thecodest.co\/contact\"><img decoding=\"async\" src=\"\/app\/uploads\/2024\/05\/interested_in_cooperation_.png\" alt=\"banner spolupr\u00e1ce\"><\/a><\/p>","protected":false},"excerpt":{"rendered":"<p>Pod\u00edvejte se na t\u0159et\u00ed d\u00edl na\u0161eho seri\u00e1lu \u010dl\u00e1nk\u016f Power of functional programming in JavaScript. Tentokr\u00e1t n\u00e1\u0161 odborn\u00edk na JavaScript vysv\u011btluje v\u00edce o funktoru a mon\u00e1d\u011b Maybe.<\/p>","protected":false},"author":2,"featured_media":3503,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"categories":[8],"tags":[],"class_list":["post-3502","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-software-development"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v27.3 (Yoast SEO v27.3) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>Functional programming in JavaScript Part 3 - Functor &amp; Monad Maybe - The Codest<\/title>\n<meta name=\"description\" content=\"Check the third part of our Power of functional programming in JavaScript article series. 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