JavaScript: Difference between revisions

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*'''Degraded accessibility''': Dynamic and/or active content is well-known to have poor accessibility for users with visual and/or cognitive impairments. While standards such as [[wikipedia:WAI-ARIA|WAI-ARIA]] were created to mitigate this, it's no silver bullet, especially when developers aren't aware of ARIA.

*'''Degraded compatibility''': While HTML and CSS degrade gracefully, meaning web browsers not supporting a certain feature will simply ignore it and load the rest of the page, JavaScript does not. If any JavaScript feature is not supported by a web browser and not caught using a <code>try</code>...<code>catch</code> block, the rest of the script is not executed, which usually breaks the entire site if it requires JavaScript for basic functions, as "web apps" usually do. This makes it impossible ~~for~~ legacy systems ~~to access a website at all~~, rather than being able to use some parts of a website.<ref>{{cite web |url=https://jakearchibald.com/2013/progressive-enhancement-still-important/ |title=Progressive enhancement is still important - JakeArchibald.com |date=2013-07-03 |access-date=2026-04-18 }}</ref>

*'''Degraded compatibility''': While HTML and CSS degrade gracefully, meaning web browsers not supporting a certain feature will simply ignore it and load the rest of the page, JavaScript does not. If any JavaScript feature is not supported by a web browser and not caught using a <code>try</code>...<code>catch</code> block, the rest of the script is not executed, which usually breaks the entire site if it requires JavaScript for basic functions, as "web apps" usually do. This makes accessing a website impossible from legacy systems that do not support recent web browser versions or minimalist web browsers that challenge the [[Google]]-[[Mozilla]] duopoly, rather than being able to use some parts of a website.<ref>{{cite web |url=https://jakearchibald.com/2013/progressive-enhancement-still-important/ |title=Progressive enhancement is still important - JakeArchibald.com |date=2013-07-03 |access-date=2026-04-18 }}</ref><ref>{{cite web |url=https://digdeeper.club/articles/browsers.xhtml#minimal |title=How to choose a browser for everyday use? § Why "minimalist" browsers suck. |author=Dig Deeper |access-date=2026-04-22 }}</ref>

*'''Lack of transparency''': To optimize network bandwidth, JS code is typically served in [[wikipedia:Minification_(programming)|minified]] form, which makes it harder to understand for humans. This is particularly problematic if the original source is not publicly [[wikipedia:Source-available_software|available]], which is typically the case of [[wikipedia:Proprietary_software|proprietary software]].<ref>{{Cite web |last=Gross |first=Carson |date=21 Sep 2023 |title=The #ViewSource Affordance |url=https://htmx.org/essays/right-click-view-source/ |url-status=live |archive-url=https://web.archive.org/web/20260228105626/https://htmx.org/essays/right-click-view-source/ |archive-date=28 Feb 2026 |access-date=24 Mar 2026 |website=</> htmx ~ Essays}}</ref>

*'''Excessive tracking''': JS is much more capable than HTML and [[CSS]]~~~~ '''combined''' to track user behavior.<ref>https://clickclickclick.click/</ref> JS can communicate with almost any server (only limited by [[wikipedia:Cross-origin_resource_sharing|CORS]]) at any time (limited by connection availability), using a plethora of protocols. JS can get hardware information and compute a [[Device fingerprint|fingerprint of the device]], user, or both.<ref>https://privacycheck.sec.lrz.de/</ref><ref>https://abrahamjuliot.github.io/creepjs</ref><ref>https://www.deviceinfo.me/</ref><ref>{{Cite web |title=Learn how identifiable you are on the Internet |url=https://www.amiunique.org/ |url-status=live |access-date=19 Mar 2026 |website=Am I Unique ?}}</ref>

*'''Excessive tracking''': JS is much more capable than HTML and [[CSS]] '''combined''' to track user behavior.<ref>https://clickclickclick.click/</ref> JS can communicate with almost any server (only limited by [[wikipedia:Cross-origin_resource_sharing|CORS]]) at any time (limited by connection availability), using a plethora of protocols. JS can get hardware information and compute a [[Device fingerprint|fingerprint of the device]], user, or both.<ref>https://privacycheck.sec.lrz.de/</ref><ref>https://abrahamjuliot.github.io/creepjs</ref><ref>https://www.deviceinfo.me/</ref><ref>{{Cite web |title=Learn how identifiable you are on the Internet |url=https://www.amiunique.org/ |url-status=live |access-date=19 Mar 2026 |website=Am I Unique ?}}</ref>

*'''Market control''': JS is built into almost every web-browser and [[wikipedia:User_agent|user-agent]] (UA), including "light-weight" ones (such as [[wikipedia:W3m|w3m]]), incentivizing companies to use it for everything, since "there's no need to worry about compatibility or portability".<ref name=":0">{{Cite web |title=Everyone has JavaScript, right? |url=https://www.kryogenix.org/code/browser/everyonehasjs |url-status=live |archive-url=https://web.archive.org/web/20260316024516/https://www.kryogenix.org/code/browser/everyonehasjs.html |archive-date=16 Mar 2026 |access-date=19 Mar 2026 |website=Kryogenix Consulting}}</ref>

*'''Security risks''': It is well-known that JS is poorly-designed,<ref>https://github.com/denysdovhan/wtfjs</ref><ref>https://github.com/brianleroux/wtfjs</ref><ref>https://github.com/Rudxain/ideas/blob/aa9a80252a4b7c9c51f32eda5c716e96220ed96e/software/evar/with_bf.js</ref> even [[wikipedia:Ecma_International|tc39]] acknowledges that{{Citation needed}}. This leads to programmers and even experienced software-devs to accidentally add vulnerabilities to their code. That, and the fact that ES is [[wikipedia:Turing_completeness|Turing-complete]] (both [https://gavinhoward.com/2024/03/what-computers-cannot-do-the-consequences-of-turing-completeness/#mathematical-vs-practical in practice and in theory]), makes [[wikipedia:Debugging|debugging]] and [[wikipedia:Reverse_engineering|reverse-engineering]] impractical in big code-bases. It's worth noting that tooling, such as [[wikipedia:TypeScript|TypeScript]] and [[wikipedia:ESLint|ESLint]], exist to substantially minimize the likelihood of [[wikipedia:Software_bug|bugs]].

*'''Degraded performance (web apps)''': "Web apps" load slower than traditional web sites because lots of code has to be processed by the web browser before any content can appear on screen, putting the content at the end of the rendering path.<ref>{{cite web |title=Critical rendering path – Mozilla Developer Network |url=https://developer.mozilla.org/en-US/docs/Web/Performance/Guides/Critical_rendering_path |access-date=2026-04-18 }}</ref>

==How it works==

Whenever a user visits a webpage, an average web-browser will execute the JS code it finds in <code><script></code> [[wikipedia:HTML_element|tags]]. This code could do anything from updating part of the [[wikipedia:Document_Object_Model|DOM]]-tree only when the user requests it, to showing a [[wikipedia:Pop-up_ad|popup/popunder]].

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===Tracking===

Many webpages (and even entire websites), force the user to keep JS enabled, otherwise they break or deliberately refuse to work. CSS stylesheets combined with HTML should be fine with most basic websites or webpages that do not need complex client side interaction.

Many webpages (and even entire websites), force the user to keep JS enabled, otherwise they break or deliberately refuse to work. CSS stylesheets combined with HTML should be fine with most basic websites/webpages that do not need complex client-side interaction or low-latency server communication.

The data collected by malicious JS makes it trivial to serve [[personalized ads]], even across unrelated sites. Some sites collect so much data that they are indistinguishable from [[spyware]] (see also [[wikipedia:Keystroke_logging|key-logging]]).<ref>{{Cite web |last=Hill |first=Kashmir |date=20 Jun 2017 |title=Before You Hit ‘Submit,’ This Company Has Already Logged Your Personal Data |url=https://gizmodo.com/before-you-hit-submit-this-company-has-already-logge-1795906081 |url-status=live |archive-url=https://web.archive.org/web/20260220091637/https://gizmodo.com/before-you-hit-submit-this-company-has-already-logge-1795906081 |archive-date=20 Feb 2026 |access-date=19 Mar 2026 |website=Gizmodo}}</ref>

===Security===

Browser-engine developers (such as [[Google]] and [[Mozilla]]) not only feel compelled, but are financially incentivized to optimize JS to its limits. This leads to complex code-bases that are harder to verify for correctness. Browser vendors mitigate this via [[wikipedia:Sandbox_(computer_security)|sandboxing]]. Unfortunately, since modern browsers compile JS to native CPU code (see [[wikipedia:Just-in-time_compilation|JIT]]) to improve performance, this introduces a higher risk of sandbox-escape.<ref>{{Cite web |last=Norman |first=Johnathan |date=4 Aug 2021 |title=Super Duper Secure Mode |url=https://microsoftedge.github.io/edgevr/posts/Super-Duper-Secure-Mode/ |url-status=live |archive-url=https://web.archive.org/web/20260218110912/https://microsoftedge.github.io/edgevr/posts/Super-Duper-Secure-Mode |archive-date=18 Feb 2026 |access-date=19 Mar 2026 |website=Microsoft Browser Vulnerability Research}}</ref> Some examples of this are as follows:

Browser-engine developers (such as Google and Mozilla) not only feel compelled, but are financially incentivized to optimize JS to its limits. This leads to complex code-bases that are harder to verify for correctness. Browser vendors mitigate this via [[wikipedia:Sandbox_(computer_security)|sandboxing]]. Unfortunately, since modern browsers compile JS to native CPU code (see [[wikipedia:Just-in-time_compilation|JIT]]) to improve performance, this introduces a higher risk of sandbox-escape.<ref>{{Cite web |last=Norman |first=Johnathan |date=4 Aug 2021 |title=Super Duper Secure Mode |url=https://microsoftedge.github.io/edgevr/posts/Super-Duper-Secure-Mode/ |url-status=live |archive-url=https://web.archive.org/web/20260218110912/https://microsoftedge.github.io/edgevr/posts/Super-Duper-Secure-Mode |archive-date=18 Feb 2026 |access-date=19 Mar 2026 |website=Microsoft Browser Vulnerability Research}}</ref> Some examples of this are as follows:

*[[wikipedia:Cross-site_scripting|XSS]], which [[wikipedia:NoScript|NoScript]] tries to mitigate

@@ Line 19: / Line 19: @@
 *'''Degraded accessibility''': Dynamic and/or active content is well-known to have poor accessibility for users with visual and/or cognitive impairments. While standards such as [[wikipedia:WAI-ARIA|WAI-ARIA]] were created to mitigate this, it's no silver bullet, especially when developers aren't aware of ARIA.
-*'''Degraded compatibility''': While HTML and CSS degrade gracefully, meaning web browsers not supporting a certain feature will simply ignore it and load the rest of the page, JavaScript does not. If any JavaScript feature is not supported by a web browser and not caught using a <code>try</code>...<code>catch</code> block, the rest of the script is not executed, which usually breaks the entire site if it requires JavaScript for basic functions, as "web apps" usually do. This makes it impossible for legacy systems to access a website at all, rather than being able to use some parts of a website.<ref>{{cite web |url=https://jakearchibald.com/2013/progressive-enhancement-still-important/ |title=Progressive enhancement is still important - JakeArchibald.com |date=2013-07-03 |access-date=2026-04-18 }}</ref>
+*'''Degraded compatibility''': While HTML and CSS degrade gracefully, meaning web browsers not supporting a certain feature will simply ignore it and load the rest of the page, JavaScript does not. If any JavaScript feature is not supported by a web browser and not caught using a <code>try</code>...<code>catch</code> block, the rest of the script is not executed, which usually breaks the entire site if it requires JavaScript for basic functions, as "web apps" usually do. This makes accessing a website impossible from legacy systems that do not support recent web browser versions or minimalist web browsers that challenge the [[Google]]-[[Mozilla]] duopoly, rather than being able to use some parts of a website.<ref>{{cite web |url=https://jakearchibald.com/2013/progressive-enhancement-still-important/ |title=Progressive enhancement is still important - JakeArchibald.com |date=2013-07-03 |access-date=2026-04-18 }}</ref><ref>{{cite web |url=https://digdeeper.club/articles/browsers.xhtml#minimal |title=How to choose a browser for everyday use? § Why "minimalist" browsers suck.  |author=Dig Deeper |access-date=2026-04-22 }}</ref>
 *'''Lack of transparency''': To optimize network bandwidth, JS code is typically served in [[wikipedia:Minification_(programming)|minified]] form, which makes it harder to understand for humans. This is particularly problematic if the original source is not publicly [[wikipedia:Source-available_software|available]], which is typically the case of [[wikipedia:Proprietary_software|proprietary software]].<ref>{{Cite web |last=Gross |first=Carson |date=21 Sep 2023 |title=The #ViewSource Affordance |url=https://htmx.org/essays/right-click-view-source/ |url-status=live |archive-url=https://web.archive.org/web/20260228105626/https://htmx.org/essays/right-click-view-source/ |archive-date=28 Feb 2026 |access-date=24 Mar 2026 |website=</> htmx ~ Essays}}</ref>
-*'''Excessive tracking''': JS is much more capable than HTML and [[CSS]]<!-- See "CSS Exfil": https://www.mike-gualtieri.com/posts/stealing-data-with-css-attack-and-defense/ --> '''combined''' to track user behavior.<ref>https://clickclickclick.click/</ref> JS can communicate with almost any server (only limited by [[wikipedia:Cross-origin_resource_sharing|CORS]]) at any time (limited by connection availability), using a plethora of protocols. JS can get hardware information and compute a [[Device fingerprint|fingerprint of the device]], user, or both.<ref>https://privacycheck.sec.lrz.de/</ref><ref>https://abrahamjuliot.github.io/creepjs</ref><ref>https://www.deviceinfo.me/</ref><ref>{{Cite web |title=Learn how identifiable you are on the Internet |url=https://www.amiunique.org/ |url-status=live |access-date=19 Mar 2026 |website=Am I Unique ?}}</ref>
+*'''Excessive tracking''': JS is much more capable than HTML and [[CSS]] '''combined''' to track user behavior.<ref>https://clickclickclick.click/</ref> JS can communicate with almost any server (only limited by [[wikipedia:Cross-origin_resource_sharing|CORS]]) at any time (limited by connection availability), using a plethora of protocols. JS can get hardware information and compute a [[Device fingerprint|fingerprint of the device]], user, or both.<ref>https://privacycheck.sec.lrz.de/</ref><ref>https://abrahamjuliot.github.io/creepjs</ref><ref>https://www.deviceinfo.me/</ref><ref>{{Cite web |title=Learn how identifiable you are on the Internet |url=https://www.amiunique.org/ |url-status=live |access-date=19 Mar 2026 |website=Am I Unique ?}}</ref>
 *'''Market control''': JS is built into almost every web-browser and [[wikipedia:User_agent|user-agent]] (UA), including "light-weight" ones (such as [[wikipedia:W3m|w3m]]), incentivizing companies to use it for everything, since "there's no need to worry about compatibility or portability".<ref name=":0">{{Cite web |title=Everyone has JavaScript, right? |url=https://www.kryogenix.org/code/browser/everyonehasjs |url-status=live |archive-url=https://web.archive.org/web/20260316024516/https://www.kryogenix.org/code/browser/everyonehasjs.html |archive-date=16 Mar 2026 |access-date=19 Mar 2026 |website=Kryogenix Consulting}}</ref><!-- We need another citation here. The current one is relevant, but doesn't cite anyone who assumes JS is portable. Ideally, it should cite an entity using that quote as an excuse to add JS everywhere -->
 *'''Security risks''': It is well-known that JS is poorly-designed,<ref>https://github.com/denysdovhan/wtfjs</ref><ref>https://github.com/brianleroux/wtfjs</ref><ref>https://github.com/Rudxain/ideas/blob/aa9a80252a4b7c9c51f32eda5c716e96220ed96e/software/evar/with_bf.js</ref> even [[wikipedia:Ecma_International|tc39]] acknowledges that{{Citation needed}}<!-- They do improve (and complicate) it every year, but the fact that `eval` isn't deprecated implies they don't care that much about improving the language -->. This leads to programmers and even experienced software-devs to accidentally add vulnerabilities to their code. That, and the fact that ES is [[wikipedia:Turing_completeness|Turing-complete]]<!-- Not typo. ECMAScript alone is TC. No need for extensions --> (both [https://gavinhoward.com/2024/03/what-computers-cannot-do-the-consequences-of-turing-completeness/#mathematical-vs-practical in practice and in theory]), makes [[wikipedia:Debugging|debugging]] and [[wikipedia:Reverse_engineering|reverse-engineering]] impractical in big code-bases. It's worth noting that tooling, such as [[wikipedia:TypeScript|TypeScript]] and [[wikipedia:ESLint|ESLint]], exist to substantially minimize the likelihood of [[wikipedia:Software_bug|bugs]].
 *'''Degraded performance (web apps)''': "Web apps" load slower than traditional web sites because lots of code has to be processed by the web browser before any content can appear on screen, putting the content at the end of the rendering path.<ref>{{cite web |title=Critical rendering path – Mozilla Developer Network |url=https://developer.mozilla.org/en-US/docs/Web/Performance/Guides/Critical_rendering_path |access-date=2026-04-18 }}</ref>
 ==How it works==
 Whenever a user visits a webpage, an average web-browser will execute the JS code it finds in <code><script></code> [[wikipedia:HTML_element|tags]]. This code could do anything from updating part of the [[wikipedia:Document_Object_Model|DOM]]-tree only when the user requests it, to showing a [[wikipedia:Pop-up_ad|popup/popunder]].
@@ Line 35: / Line 36: @@
 ===Tracking===
-Many webpages (and even entire websites), force the user to keep JS enabled, otherwise they break or deliberately refuse to work. CSS stylesheets combined with HTML<!-- TO-DO: cite `<portal>`. I remember an entire website that demos/showcases the Portal API, but can't find it. `<portal>` fixed the fundamental problem that SPAs try to solve, with minimal (or zero!) JS --> should be fine with most basic websites or webpages that do not need complex client side interaction.
+Many webpages (and even entire websites), force the user to keep JS enabled, otherwise they break or deliberately refuse to work. CSS stylesheets combined with HTML<!-- TO-DO: cite `<portal>`. I remember an entire website that demos/showcases the Portal API, but can't find it. `<portal>` fixed the fundamental problem that SPAs try to solve, with minimal (or zero!) JS --> should be fine with most basic websites/webpages that do not need complex client-side interaction or low-latency server communication.<!-- see Web-Sockets -->
 The data collected by malicious JS makes it trivial to serve [[personalized ads]], even across unrelated sites. Some sites collect so much data that they are indistinguishable from [[spyware]] (see also [[wikipedia:Keystroke_logging|key-logging]]).<ref>{{Cite web |last=Hill |first=Kashmir |date=20 Jun 2017 |title=Before You Hit ‘Submit,’ This Company Has Already Logged Your Personal Data |url=https://gizmodo.com/before-you-hit-submit-this-company-has-already-logge-1795906081 |url-status=live |archive-url=https://web.archive.org/web/20260220091637/https://gizmodo.com/before-you-hit-submit-this-company-has-already-logge-1795906081 |archive-date=20 Feb 2026 |access-date=19 Mar 2026 |website=Gizmodo}}</ref>
 ===Security===
-Browser-engine developers (such as [[Google]] and [[Mozilla]]) not only feel compelled, but are financially incentivized to optimize JS to its limits. This leads to complex code-bases that are harder to verify for correctness. Browser vendors mitigate this via [[wikipedia:Sandbox_(computer_security)|sandboxing]]. Unfortunately, since modern browsers compile JS to native CPU code (see [[wikipedia:Just-in-time_compilation|JIT]]) to improve performance, this introduces a higher risk of sandbox-escape.<ref>{{Cite web |last=Norman |first=Johnathan |date=4 Aug 2021 |title=Super Duper Secure Mode |url=https://microsoftedge.github.io/edgevr/posts/Super-Duper-Secure-Mode/ |url-status=live |archive-url=https://web.archive.org/web/20260218110912/https://microsoftedge.github.io/edgevr/posts/Super-Duper-Secure-Mode |archive-date=18 Feb 2026 |access-date=19 Mar 2026 |website=Microsoft Browser Vulnerability Research}}</ref> Some examples of this are as follows:
+Browser-engine developers (such as Google and Mozilla) not only feel compelled, but are financially incentivized to optimize JS to its limits. This leads to complex code-bases that are harder to verify for correctness. Browser vendors mitigate this via [[wikipedia:Sandbox_(computer_security)|sandboxing]]. Unfortunately, since modern browsers compile JS to native CPU code (see [[wikipedia:Just-in-time_compilation|JIT]]) to improve performance, this introduces a higher risk of sandbox-escape.<ref>{{Cite web |last=Norman |first=Johnathan |date=4 Aug 2021 |title=Super Duper Secure Mode |url=https://microsoftedge.github.io/edgevr/posts/Super-Duper-Secure-Mode/ |url-status=live |archive-url=https://web.archive.org/web/20260218110912/https://microsoftedge.github.io/edgevr/posts/Super-Duper-Secure-Mode |archive-date=18 Feb 2026 |access-date=19 Mar 2026 |website=Microsoft Browser Vulnerability Research}}</ref> Some examples of this are as follows:
 *[[wikipedia:Cross-site_scripting|XSS]], which [[wikipedia:NoScript|NoScript]] tries to mitigate