{"id":3044,"date":"2020-09-02T08:51:00","date_gmt":"2020-09-02T08:51:00","guid":{"rendered":"http:\/\/the-codest.localhost\/blog\/asynchronous-and-single-threaded-javascript-meet-the-event-loop\/"},"modified":"2026-04-24T11:34:04","modified_gmt":"2026-04-24T11:34:04","slug":"asynkront-och-enkeltradigt-javascript-moter-handelseslingan","status":"publish","type":"post","link":"https:\/\/thecodest.co\/sv\/blog\/asynchronous-and-single-threaded-javascript-meet-the-event-loop\/","title":{"rendered":"Asynkron och enkeltr\u00e5dad JavaScript?"},"content":{"rendered":"<ul class=\"wp-block-list\">\n<li><strong>Runtid<\/strong><\/li>\n<\/ul>\n\n\n\n<p><a href=\"https:\/\/thecodest.co\/sv\/blog\/hire-javascript-developer\/\">JavaScript<\/a> \u00e4r ett tolkat spr\u00e5k, inte ett kompilerat. Det betyder att det beh\u00f6ver en tolk som omvandlar <a href=\"https:\/\/thecodest.co\/sv\/blog\/hire-vue-js-developers\/\">JS<\/a> <a href=\"https:\/\/thecodest.co\/sv\/dictionary\/what-is-code-refactoring\/\">kod<\/a> till en maskinkod. Det finns flera olika typer av tolkar (s.k. motorer). De mest popul\u00e4ra webbl\u00e4sarmotorerna \u00e4r V8 (Chrome), Quantum (Firefox) och WebKit (Safari). V8 anv\u00e4nds f\u00f6r \u00f6vrigt ocks\u00e5 i en popul\u00e4r runtime som inte \u00e4r f\u00f6r webbl\u00e4sare, <a href=\"https:\/\/thecodest.co\/sv\/blog\/find-your-node-js-expert-for-hire-today\/\">Node.js<\/a>.<\/p>\n\n\n\n<p>Varje motor inneh\u00e5ller en minnesh\u00f6g, en anropsstack, en h\u00e4ndelseslinga, en \u00e5teruppringningsk\u00f6 och ett WebAPI med HTTP-f\u00f6rfr\u00e5gningar, timers, h\u00e4ndelser etc., allt implementerat p\u00e5 sitt eget s\u00e4tt f\u00f6r snabbare och s\u00e4krare tolkning av JS-koden.<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"\/app\/uploads\/2024\/05\/runtime-architecture.png\" alt=\"JavaScript utveckling\" title=\"JavaScript utveckling\"\/><\/figure>\n\n\n\n<p><em>Grundl\u00e4ggande JS runtime-arkitektur. F\u00f6rfattare: Alex Zlatkov<\/em><\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>Enstaka tr\u00e5d<\/strong><\/h2>\n\n\n\n<p>Ett spr\u00e5k med en enda tr\u00e5d \u00e4r ett spr\u00e5k med en enda anropsstack och en enda minnesh\u00f6g. Det betyder att det bara k\u00f6r en sak \u00e5t g\u00e5ngen.<\/p>\n\n\n\n<p>A&nbsp;<code>stack<\/code>&nbsp;\u00e4r en kontinuerlig minnesregion som allokerar en lokal kontext f\u00f6r varje exekverad funktion.<\/p>\n\n\n\n<p>A&nbsp;<code>h\u00f6g<\/code>&nbsp;\u00e4r en mycket st\u00f6rre region som lagrar allt som allokeras dynamiskt.<\/p>\n\n\n\n<p>A&nbsp;<code>anropsstapel<\/code>&nbsp;\u00e4r en <a href=\"https:\/\/thecodest.co\/sv\/blog\/app-data-collection-security-risks-value-and-types-explored\/\">data<\/a> struktur som i princip registrerar var vi befinner oss i programmet.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Samtalsstack<\/strong><\/h3>\n\n\n\n<p>L\u00e5t oss skriva en enkel kod och f\u00f6lja vad som h\u00e4nder i anropsstacken.<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"\/app\/uploads\/2024\/05\/stack.gif\" alt=\"JavaScript mjukvaruutveckling\" title=\"JavaScript mjukvaruutveckling\"\/><\/figure>\n\n\n\n<p>Som du kan se l\u00e4ggs funktionerna till i stacken, utf\u00f6rs och tas sedan bort. Det \u00e4r det s\u00e5 kallade LIFO-s\u00e4ttet - Last In, First Out. Varje post i anropsstacken kallas en&nbsp;<code>stapelram<\/code>.<\/p>\n\n\n\n<p>Kunskap om anropsstacken \u00e4r anv\u00e4ndbar f\u00f6r att l\u00e4sa felstacksp\u00e5r. I allm\u00e4nhet st\u00e5r den exakta orsaken till felet h\u00f6gst upp p\u00e5 f\u00f6rsta raden, \u00e4ven om ordningen p\u00e5 kodk\u00f6rningen \u00e4r nedifr\u00e5n och upp.<\/p>\n\n\n\n<p>Ibland kan du hantera ett popul\u00e4rt fel, meddelat av\u00a0<code>Maximal storlek p\u00e5 anropsstacken \u00f6verskriden<\/code>. Det \u00e4r l\u00e4tt att f\u00e5 detta med hj\u00e4lp av rekursion:<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"javascript\" class=\"language-javascript\">funktion foo() {\n    foo()\n}\nfoo()<\/code><\/pre>\n\n\n\n<p>och v\u00e5r webbl\u00e4sare eller terminal fryser. Varje webbl\u00e4sare, \u00e4ven deras olika versioner, har en annan gr\u00e4ns f\u00f6r anropsstackens storlek. I de allra flesta fall \u00e4r de tillr\u00e4ckliga och problemet b\u00f6r s\u00f6kas n\u00e5gon annanstans.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Stack f\u00f6r blockerade samtal<\/strong><\/h3>\n\n\n\n<p>H\u00e4r \u00e4r ett exempel p\u00e5 blockering av JS-tr\u00e5den. L\u00e5t oss f\u00f6rs\u00f6ka l\u00e4sa en&nbsp;<code>Foo<\/code>&nbsp;fil och en&nbsp;<code>bar<\/code>&nbsp;med hj\u00e4lp av <a href=\"https:\/\/thecodest.co\/sv\/dictionary\/what-is-node-js-used-for\/\">Nod<\/a>.js synkron funktion&nbsp;<code>readFileSync<\/code>.<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"\/app\/uploads\/2024\/05\/blocking.gif\" alt=\"JavaScript kod\" title=\"JavaScript kod\"\/><\/figure>\n\n\n\n<p>Detta \u00e4r en loopad GIF. Som du ser v\u00e4ntar JS-motorn tills det f\u00f6rsta anropet i&nbsp;<code>readFileSync<\/code>&nbsp;\u00e4r slutf\u00f6rd. Men detta kommer inte att ske eftersom det inte finns n\u00e5gon&nbsp;<code>Foo<\/code>&nbsp;filen, s\u00e5 den andra funktionen kommer aldrig att anropas.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>Asynkront beteende<\/strong><\/h2>\n\n\n\n<p>JS kan dock ocks\u00e5 vara icke-blockerande och bete sig som om den vore flertr\u00e5dig. Det inneb\u00e4r att den inte v\u00e4ntar p\u00e5 svaret fr\u00e5n en <a href=\"https:\/\/thecodest.co\/sv\/blog\/compare-staff-augmentation-firms-that-excel-in-api-team-staffing-for-financial-technology-projects\/\">API<\/a> anrop, I\/O-h\u00e4ndelser etc. och kan forts\u00e4tta att exekvera koden. Det \u00e4r m\u00f6jligt tack vare JS-motorerna som anv\u00e4nder (under huven) riktiga multitr\u00e5dningsspr\u00e5k, som C++ (Chrome) eller Rust (Firefox). De tillhandah\u00e5ller <a href=\"https:\/\/thecodest.co\/sv\/blog\/why-us-companies-are-opting-for-polish-developers\/\">oss<\/a> med <a href=\"https:\/\/thecodest.co\/sv\/blog\/find-your-ideal-stack-for-web-development\/\">Webb<\/a> API under webbl\u00e4sarens huvar eller ex. I\/O API under Node.js.<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"\/app\/uploads\/2024\/05\/callback-queue.gif\" alt=\"JavaScript programmeringsspr\u00e5k\" title=\"JavaScript programmeringsspr\u00e5k\"\/><\/figure>\n\n\n\n<p>I GIF:en ovan ser vi att den f\u00f6rsta funktionen flyttas till anropsstacken och&nbsp;<code>Hej<\/code>&nbsp;k\u00f6rs omedelbart i konsolen.<\/p>\n\n\n\n<p>Sedan kallar vi&nbsp;<code>setTimeout<\/code>&nbsp;funktion som tillhandah\u00e5lls av webbl\u00e4sarens WebAPI. Den g\u00e5r till anropsstacken och dess asynkrona \u00e5teruppringning&nbsp;<code>Foo<\/code>&nbsp;funktionen g\u00e5r till WebApi-k\u00f6n, d\u00e4r den v\u00e4ntar p\u00e5 anropet, som \u00e4r inst\u00e4llt p\u00e5 att ske efter 3 sekunder.<\/p>\n\n\n\n<p>Under tiden forts\u00e4tter programmet koden och vi ser&nbsp;<code>Hej. Jag \u00e4r inte blockerad<\/code>&nbsp;i konsolen.<\/p>\n\n\n\n<p>Efter att den har anropats g\u00e5r varje funktion i WebAPI-k\u00f6n till&nbsp;<code>K\u00f6 f\u00f6r \u00e5teruppringning<\/code>. Det \u00e4r d\u00e4r funktioner v\u00e4ntar tills anropsstacken \u00e4r tom. N\u00e4r det sker flyttas de dit en efter en.<\/p>\n\n\n\n<p>S\u00e5 n\u00e4r v\u00e5r&nbsp;<code>setTimeout<\/code>&nbsp;timern avslutar nedr\u00e4kningen, kommer v\u00e5r&nbsp;<code>Foo<\/code>&nbsp;funktionen g\u00e5r till \u00e5teruppringningsk\u00f6n, v\u00e4ntar tills anropsstacken blir tillg\u00e4nglig, g\u00e5r dit, exekveras och vi ser&nbsp;<code>Hej fr\u00e5n asynkron callback<\/code>&nbsp;i konsolen.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Evenemangsslinga<\/strong><\/h3>\n\n\n\n<p>Fr\u00e5gan \u00e4r hur runtime vet att anropsstacken \u00e4r tom och hur h\u00e4ndelsen i callback-k\u00f6n anropas? M\u00f6t h\u00e4ndelseslingan. Det \u00e4r en del av JS-motorn. Den h\u00e4r processen kontrollerar st\u00e4ndigt om anropsstacken \u00e4r tom och, om den \u00e4r det, \u00f6vervakar om det finns en h\u00e4ndelse i \u00e5teruppringningsk\u00f6n som v\u00e4ntar p\u00e5 att bli anropad.<\/p>\n\n\n\n<p>Det \u00e4r all magi bakom kulisserna!<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>Sammanfattning av teorin<\/strong><\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Samtidighet och parallellism<\/strong><\/h3>\n\n\n\n<p><code>Samtidighet<\/code>&nbsp;inneb\u00e4r att man utf\u00f6r flera uppgifter samtidigt men inte samtidigt. T.ex. tv\u00e5 arbetsuppgifter som utf\u00f6rs under \u00f6verlappande tidsperioder.<\/p>\n\n\n\n<p><code>Parallellism<\/code>&nbsp;inneb\u00e4r att utf\u00f6ra tv\u00e5 eller flera uppgifter samtidigt, t.ex. att utf\u00f6ra flera ber\u00e4kningar samtidigt.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Tr\u00e5dar och processer<\/strong><\/h3>\n\n\n\n<p><code>Tr\u00e5dar<\/code>&nbsp;\u00e4r en sekvens av kodexekveringar som kan utf\u00f6ras oberoende av varandra.<\/p>\n\n\n\n<p><code>Process<\/code>&nbsp;\u00e4r en instans av ett program som k\u00f6rs. Ett program kan ha flera processer.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Synkron och asynkron<\/strong><\/h3>\n\n\n\n<p>I&nbsp;<code>synkron<\/code>&nbsp;Vid programmering utf\u00f6rs uppgifterna efter varandra. Varje uppgift v\u00e4ntar p\u00e5 att en tidigare uppgift ska bli klar och utf\u00f6rs f\u00f6rst d\u00e5.<\/p>\n\n\n\n<p>I&nbsp;<code>asynkron<\/code>&nbsp;programmering, n\u00e4r en uppgift \u00e4r utf\u00f6rd kan du v\u00e4xla till en annan uppgift utan att v\u00e4nta p\u00e5 att den f\u00f6reg\u00e5ende ska bli klar.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Synkron och asynkron i en enkel- och flertr\u00e5dad milj\u00f6<\/strong><\/h3>\n\n\n\n<p><code>Synkron med en enda tr\u00e5d<\/code>: Uppgifterna utf\u00f6rs en efter en. Varje uppgift v\u00e4ntar p\u00e5 att den f\u00f6reg\u00e5ende uppgiften ska bli utf\u00f6rd.<\/p>\n\n\n\n<p><code>Synkron med flera tr\u00e5dar<\/code>: Uppgifter utf\u00f6rs i olika tr\u00e5dar men v\u00e4ntar p\u00e5 andra uppgifter som utf\u00f6rs i n\u00e5gon annan tr\u00e5d.<\/p>\n\n\n\n<p><code>Asynkron med en enda tr\u00e5d<\/code>: Uppgifter b\u00f6rjar utf\u00f6ras utan att v\u00e4nta p\u00e5 att en annan uppgift ska bli klar. Vid en given tidpunkt kan endast en enda uppgift utf\u00f6ras.<\/p>\n\n\n\n<p><code>Asynkron med flera tr\u00e5dar<\/code>: Uppgifter utf\u00f6rs i olika tr\u00e5dar utan att v\u00e4nta p\u00e5 att andra uppgifter ska slutf\u00f6ras och avslutar sina k\u00f6rningar oberoende av varandra.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>JavaScript klassificering<\/strong><\/h2>\n\n\n\n<p>Om vi tittar p\u00e5 hur JS-motorerna fungerar under huven kan vi klassificera JS som ett asynkront och enkeltr\u00e5dat tolkat spr\u00e5k. Ordet \"tolkat\" \u00e4r mycket viktigt eftersom det inneb\u00e4r att spr\u00e5ket alltid kommer att vara runtime-beroende och aldrig lika snabbt som kompilerade spr\u00e5k med inbyggd multi-threading.<\/p>\n\n\n\n<p>Det \u00e4r v\u00e4rt att notera att Node.js kan \u00e5stadkomma verklig multi-threading, f\u00f6rutsatt att varje tr\u00e5d startas som en separat process. Det finns bibliotek f\u00f6r detta, men Node.js har en inbyggd funktion som heter&nbsp;<a href=\"https:\/\/nodejs.org\/api\/worker_threads.html#worker_threads_worker_threads\">Arbetartr\u00e5dar<\/a>.<\/p>\n\n\n\n<p>Alla GIF-bilder fr\u00e5n evenemangsslingan kommer fr\u00e5n&nbsp;<a href=\"https:\/\/github.com\/latentflip\/loupe\">Loupe<\/a>&nbsp;applikation skapad av Philip Roberts, d\u00e4r du kan testa dina asynkrona scenarier.<\/p>\n\n\n\n<p><b>L\u00e4s mer om detta:<\/b><\/p>\n\n\n\n<p><a href=\"https:\/\/thecodest.co\/blog\/why-you-should-probably-use-typescript\">Varf\u00f6r b\u00f6r du (f\u00f6rmodligen) anv\u00e4nda Typescript?<\/a><\/p>\n\n\n\n<p><a href=\"https:\/\/thecodest.co\/blog\/quality-first-5-easy-steps-to-lint-your-code-with-github-workflows-in-javascript-project\/\">Kvalitet f\u00f6rst! 5 enkla steg f\u00f6r att linta din kod med GitHub-arbetsfl\u00f6den i JavaScript-projektet<\/a><\/p>\n\n\n\n<p><a href=\"https:\/\/thecodest.co\/blog\/how-to-improve-vue-js-apps-some-practical-tips\/\">Hur kan man f\u00f6rb\u00e4ttra Vue.js-appar? N\u00e5gra praktiska tips<\/a><\/p>","protected":false},"excerpt":{"rendered":"<p>JavaScript \u00e4r ett enkeltr\u00e5dat spr\u00e5k och samtidigt ocks\u00e5 icke-blockerande, asynkront och samtidigt. Den h\u00e4r artikeln kommer att f\u00f6rklara f\u00f6r dig hur det h\u00e4nder.<\/p>","protected":false},"author":2,"featured_media":3045,"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-3044","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>Asynchronous and Single-threaded JavaScript? - The Codest<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/thecodest.co\/sv\/blogg\/asynkront-och-enkeltradigt-javascript-moter-handelseslingan\/\" \/>\n<meta property=\"og:locale\" content=\"sv_SE\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Asynchronous and Single-threaded JavaScript?\" \/>\n<meta property=\"og:description\" content=\"JavaScript is a single-threaded language and, at the same time, also non-blocking, asynchronous and concurrent. 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