Sunday, May 26, 2024

What SEOs Actually Have to Know About JavaScript website positioning

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Do you know that whereas the Ahrefs Weblog is powered by WordPress, a lot of the remainder of the positioning is powered by JavaScript like React?

The truth of the present internet is that JavaScript is all over the place. Most web sites use some form of JavaScript so as to add interactivity and enhance person expertise. 

But a lot of the JavaScript used on so many web sites gained’t affect website positioning in any respect. You probably have a standard WordPress set up with out loads of customization, then doubtless not one of the points will apply to you.

The place you’ll run into points is when JavaScript is used to construct a complete web page, add or take away components, or change what was already on the web page. Some websites use it for menus, pulling in merchandise or costs, grabbing content material from a number of sources or, in some instances, for all the things on the positioning. If this feels like your website, hold studying.

We’re seeing total programs and apps constructed with JavaScript frameworks and even some conventional CMSes with a JavaScript aptitude the place they’re headless or decoupled. The CMS is used because the backend supply of information, however the frontend presentation is dealt with by JavaScript.

I’m not saying that SEOs must exit and discover ways to program JavaScript. I really don’t suggest it as a result of it’s not going that you’ll ever contact the code. What SEOs must know is how Google handles JavaScript and tips on how to troubleshoot points. 

JavaScript website positioning is part of technical website positioning (search engine marketing) that makes JavaScript-heavy web sites simple to crawl and index, in addition to search-friendly. The objective is to have these web sites be discovered and rank greater in serps.

JavaScript is just not unhealthy for website positioning, and it’s not evil. It’s simply totally different from what many SEOs are used to, and there’s a little bit of a studying curve. 

A number of the processes are much like issues SEOs are already used to seeing, however there could also be slight variations. You’re nonetheless going to be principally HTML code, not really JavaScript.

All the conventional on-page website positioning greatest practices nonetheless apply. See our information on on-page website positioning.

You’ll even discover acquainted plugin-type choices to deal with loads of the essential website positioning components, if it’s not already constructed into the framework you’re utilizing. For JavaScript frameworks, these are referred to as modules, and also you’ll discover a number of package deal choices to put in them.

There are variations for lots of the widespread frameworks like React, Vue, Angular, and Svelte that you’ll find by trying to find the framework + module identify like “React Helmet.” Meta tags, Helmet, and Head are all widespread modules with related performance and permit for lots of the widespread tags wanted for website positioning to be set.

In some methods, JavaScript is best than conventional HTML, corresponding to ease of constructing and efficiency. In some methods, JavaScript is worse, corresponding to it may’t be parsed progressively (like HTML and CSS will be), and it may be heavy on web page load and efficiency. Typically, chances are you’ll be buying and selling efficiency for performance.

JavaScript isn’t excellent, and it isn’t at all times the suitable instrument for the job. Builders do overuse it for issues the place there’s in all probability a greater resolution. However typically, it’s important to work with what you’re given.

JavaScript website positioning points and greatest practices

These are lots of the frequent website positioning points chances are you’ll run into when working with JavaScript websites.

Have distinctive title tags and meta descriptions

You’re nonetheless going to need to have distinctive title tags and meta descriptions throughout your pages. As a result of loads of the JavaScript frameworks are templatized, you’ll be able to simply find yourself in a scenario the place the identical title or meta description is used for all pages or a gaggle of pages.

Examine the Duplicates report in Ahrefs’ Web site Audit and click on into any of the groupings to see extra knowledge concerning the points we discovered.

Checking for duplicate title tags and meta descriptions

You should utilize one of many website positioning modules like Helmet to set customized tags for every web page.

JavaScript can be used to overwrite default values you could have set. Google will course of this and use the overwritten title or description. For customers, nevertheless, titles will be problematic, as one title might seem within the browser they usually’ll discover a flash when it will get overwritten.

Should you see the title flashing, you should use Ahrefs’ website positioning Toolbar to see each the uncooked HTML and rendered variations.

Raw and rendered titles and meta descriptions in Ahrefs' SEO Toolbar

Google might not use your titles or meta descriptions anyway. As I discussed, the titles are value cleansing up for customers. Fixing this for meta descriptions gained’t actually make a distinction, although.

Once we studied Google’s rewriting, we discovered that Google overwrites titles 33.4% of the time and meta descriptions 62.78% of the time. In Web site Audit, we’ll even present you which of them of your title tags Google has modified.

"Page and SERP titles do not match" issue in Ahrefs' Site Audit

Canonical tag points

For years, Google mentioned it didn’t respect canonical tags inserted with JavaScript. It lastly added an exception to the documentation for instances the place there wasn’t already a tag. I precipitated that change. I ran assessments to point out this labored when Google was telling everybody it didn’t.

If there was already a canonical tag current and also you add one other one or overwrite the prevailing one with JavaScript, then you definitely’re giving them two canonical tags. On this case, Google has to determine which one to make use of or ignore the canonical tags in favor of different canonicalization alerts.

Commonplace website positioning recommendation of “each web page ought to have a self-referencing canonical tag” will get many SEOs in bother. A dev takes that requirement, they usually make pages with and and not using a trailing slash self-canonical. page with a canonical of page and page/ with a canonical of page/. Oops, that’s mistaken! You in all probability need to redirect a kind of variations to the different.

The identical factor can occur with parameterized variations that you could be need to mix, however every is self-referencing.

Google makes use of essentially the most restrictive meta robots tag

With meta robots tags, Google is at all times going to take essentially the most restrictive choice it sees—irrespective of the placement. 

You probably have an index tag within the uncooked HTML and noindex tag within the rendered HTML, Google will deal with it as noindex. You probably have a noindex tag within the uncooked HTML however you overwrite it with an index tag utilizing JavaScript, it’s nonetheless going to deal with that web page as noindex.

It really works the identical for nofollow tags. Google goes to take essentially the most restrictive choice. 

Set alt attributes on photographs

Lacking alt attributes are an accessibility concern, which can flip right into a authorized concern. Most massive corporations have been sued for ADA compliance points on their web sites, and a few get sued a number of instances a yr. I’d repair this for the primary content material photographs, however not for issues like placeholder or ornamental photographs the place you’ll be able to go away the alt attributes clean.

For internet search, the textual content in alt attributes counts as textual content on the web page, however that’s actually the one position it performs. Its significance is usually overstated for website positioning, for my part. Nonetheless, it does assist with picture search and picture rankings.

A lot of JavaScript builders go away alt attributes clean, so double-check that yours are there. Have a look at the Photos report in Web site Audit to seek out these.

Checking for missing alt attributes on JavaScript-powered sites

Permit crawling of JavaScript recordsdata

Don’t block entry to assets if they’re wanted to construct a part of the web page or add to the content material. Google must entry and obtain assets in order that it may render the pages correctly. In your robots.txt, the simplest approach to enable the wanted assets to be crawled is to add:

Consumer-Agent: Googlebot
Permit: .js
Permit: .css

Additionally examine the robots.txt recordsdata for any subdomains or extra domains chances are you’ll be making requests from, corresponding to these on your API calls.

You probably have blocked assets with robots.txt, you’ll be able to examine if it impacts the web page content material utilizing the block choices within the “Community” tab in Chrome Dev Instruments. Choose the file and block it, then reload the web page to see if any modifications have been made.

"Block request URL" option in dropdown

Examine if Google sees your content material

Many pages with JavaScript performance will not be exhibiting all the content material to Google by default. Should you discuss to your builders, they might consult with this as being not Doc Object Mannequin (DOM) loaded. This implies the content material wasn’t loaded by default and is perhaps loaded later with an motion like a click on.

A fast examine you are able to do is to easily seek for a snippet of your content material in Google inside citation marks. Seek for “some phrase out of your content material” and see if the web page is returned within the search outcomes. Whether it is, then your content material was doubtless seen.


Content material that’s hidden by default will not be proven inside your snippet on the SERPs. It’s particularly essential to examine your cellular model, as that is usually stripped down for person expertise.

It’s also possible to right-click and use the “Examine” choice. Seek for the textual content throughout the “Components” tab.

Searching for text in the DOM when working with JavaScript websites

One of the best examine goes to be looking throughout the content material of considered one of Google’s testing instruments just like the URL Inspection instrument in Google Search Console. I’ll discuss extra about this later.

I’d positively examine something behind an accordion or a dropdown. Typically, these components make requests that load content material into the web page when they’re clicked on. Google doesn’t click on, so it doesn’t see the content material.

Should you use the examine technique to go looking content material, ensure that to repeat the content material after which reload the web page or open it in an incognito window earlier than looking. 

Should you’ve clicked the component and the content material loaded in when that motion was taken, you’ll discover the content material. You might not see the identical outcome with a recent load of the web page.

Duplicate content material points

With JavaScript, there could also be a number of URLs for a similar content material, which ends up in duplicate content material points. This can be brought on by capitalization, trailing slashes, IDs, parameters with IDs, and so on. So all of those might exist:

Should you solely need one model listed, it’s best to set a self-referencing canonical and both canonical tags from different variations that reference the primary model or ideally redirect the opposite variations to the primary model.

Examine the Duplicates report in Web site Audit. We break down which duplicate clusters have canonical tags set and which have points.

Duplicate content clusters within Ahrefs' Site Audit

A typical concern with JavaScript frameworks is that pages can exist with and with out the trailing slash. Ideally, you’d choose the model you favor and ensure that model has a self-referencing canonical tag after which redirect the opposite model to your most popular model.

With app shell fashions, little or no content material and code could also be proven within the preliminary HTML response. Actually, each web page on the positioning might show the identical code, and this code could also be the very same because the code on another web sites. 

Should you see loads of URLs with a low phrase rely in Web site Audit, it might point out you’ve this concern. 

URLs by word count report in Ahrefs' Site Audit

This will typically trigger pages to be handled as duplicates and never instantly go to rendering. Even worse, the mistaken web page and even the mistaken website might present in search outcomes. This could resolve itself over time however will be problematic, particularly with newer web sites.

Don’t use fragments (#) in URLs

# already has an outlined performance for browsers. It hyperlinks to a different a part of a web page when clicked—like our “desk of contents” function on the weblog. Servers usually gained’t course of something after a #. So for a URL like thing, something after a # is often ignored. 

JavaScript builders have determined they need to use # because the set off for various functions, and that causes confusion. The most typical methods they’re misused are for routing and for URL parameters. Sure, they work. No, you shouldn’t do it.

JavaScript frameworks usually have routers that map what they name routes (paths) to wash URLs. A number of JavaScript builders use hashes (#) for routing. That is particularly an issue for Vue and a few of the earlier variations of Angular. 

To repair this for Vue, you’ll be able to work along with your developer to vary the next:

Vue router: 
Use ‘Historical past’ Mode as an alternative of the standard ‘Hash’ Mode.

const router = new VueRouter ({
mode: ‘historical past’,
router: [] //the array of router hyperlinks

There’s a rising development the place individuals are utilizing # as an alternative of ? because the fragment identifier, particularly for passive URL parameters like these used for monitoring. I are inclined to suggest towards it due to all the confusion and points. Situationally, I is perhaps OK with it eliminating loads of pointless parameters.

Create a sitemap

The router choices that enable for clear URLs often have an extra module that may additionally create sitemaps. You will discover them by trying to find your system + router sitemap, corresponding to “Vue router sitemap.” 

Lots of the rendering options might also have sitemap choices. Once more, simply discover the system you utilize and Google the system + sitemap corresponding to “Gatsby sitemap,” and also you’re positive to discover a resolution that already exists.

Standing codes and gentle 404s

As a result of JavaScript frameworks aren’t server-side, they will’t actually throw a server error like a 404. You might have a few totally different choices for error pages, such as:

  1. Utilizing a JavaScript redirect to a web page that does reply with a 404 standing code.
  2. Including a noindex tag to the web page that’s failing together with some form of error message like “404 Web page Not Discovered.” This might be handled as a gentle 404 because the precise standing code returned might be a 200 okay.

JavaScript redirects are OK, however not most popular

SEOs are used to 301/302 redirects, that are server-side. JavaScript is often run client-side. Server-side redirects and even meta refresh redirects might be simpler for Google to course of than JavaScript redirects because it gained’t should render the web page to see them.

JavaScript redirects will nonetheless be seen and processed throughout rendering and must be OK usually—they’re simply not as very best as different redirect sorts. They’re handled as everlasting redirects and nonetheless go all alerts like PageRank.

You’ll be able to usually discover these redirects within the code by searching for “window.location.href”. The redirects might probably be within the config file as effectively. Within the Subsequent.js config, there’s a redirect operate you should use to set redirects. In different programs, chances are you’ll discover them within the router.

Internationalization points

There are often a couple of module choices for various frameworks that assist some options wanted for internationalization like hreflang. They’ve generally been ported to the totally different programs and embrace i18n, intl or, many instances, the identical modules used for header tags like Helmet can be utilized so as to add the wanted tags.

We flag hreflang points within the Localization report in Web site Audit. We additionally ran a research and located that 67% of domains utilizing hreflang have points.

Hreflang issues shown in Ahrefs' Site Audit

You additionally should be cautious in case your website is obstructing or treating guests from a selected nation or utilizing a selected IP in several methods. This will trigger your content material to not be seen by Googlebot. You probably have logic redirecting customers, chances are you’ll need to exclude bots from this logic.

We’ll let you recognize if that is occurring when organising a undertaking in Web site Audit.

Checking if JavaScript site is being redirected

Use structured knowledge

JavaScript can be utilized to generate or to inject structured knowledge in your pages. It’s fairly frequent to do that with JSON-LD and never more likely to trigger any points, however run some assessments to verify all the things comes out such as you count on.

We’ll flag any structured knowledge we see within the Points report in Web site Audit. Search for the “Structured knowledge has validation” error. We’ll let you know precisely what’s mistaken for every web page.

Making sure schema markup is valid

Use normal format hyperlinks

Hyperlinks to different pages must be within the internet normal format. Inner and exterior hyperlinks should be an <a> tag with an href attribute. There are lots of methods you can also make hyperlinks work for customers with JavaScript that aren’t search-friendly.


<a href=”/web page”>easy is sweet</a>

<a href=”/web page” onclick=”goTo(‘web page’)”>nonetheless okay</a>


<a onclick=”goTo(‘web page’)”>nope, no href</a>

<a href=”javascript:goTo(‘web page’)”>nope, lacking hyperlink</a>

<a href=”javascript:void(0)”>nope, lacking hyperlink</a>

<span onclick=”goTo(‘web page’)”>not the suitable HTML component</span>

<choice worth="web page">nope, mistaken HTML component</choice>

<a href=”#”>no hyperlink</a>

Button, ng-click, there are various extra methods this may be completed incorrectly.

In my expertise, Google nonetheless processes lots of the unhealthy hyperlinks and crawls them, however I’m undecided the way it treats them as far passing alerts like PageRank. The net is a messy place, and Google’s parsers are sometimes pretty forgiving.

It’s additionally value noting that inside hyperlinks added with JavaScript won’t get picked up till after rendering. That must be comparatively fast and never a trigger for concern in most instances.

Use file versioning to unravel for not possible states being listed

Google closely caches all assets on its finish. I’ll speak about this a bit extra later, however it’s best to know that its system can result in some not possible states being listed. It is a quirk of its programs. In these instances, earlier file variations are used within the rendering course of, and the listed model of a web page might include elements of older recordsdata.

You should utilize file versioning or fingerprinting (file.12345.js) to generate new file names when vital modifications are made in order that Google has to obtain the up to date model of the useful resource for rendering.

You might not see what’s proven to Googlebot

You might want to vary your user-agent to correctly diagnose some points. Content material will be rendered otherwise for various user-agents and even IPs. It is best to examine what Google really sees with its testing instruments, and I’ll cowl these in a bit.

You’ll be able to set a customized user-agent with Chrome DevTools to troubleshoot websites that prerender based mostly on particular user-agents, or you’ll be able to simply do that with our toolbar as effectively.

Switching user-agent to troubleshoot SEO issues on JavaScript sites

Use polyfills for unsupported options

There will be options utilized by builders that Googlebot doesn’t assist. Your builders can use function detection. And if there’s a lacking function, they will select to both skip that performance or use a fallback technique with a polyfill to see if they will make it work.

That is principally an FYI for SEOs. Should you see one thing you suppose Google must be seeing and it’s not seeing it, it could possibly be due to the implementation. 

Use lazy loading

Since I initially wrote this, lazy loading has principally moved from being JavaScript-driven to being dealt with by browsers.

You should still run into some JavaScript-driven lazy load setups. For essentially the most half, they’re in all probability superb if the lazy loading is for photographs. The principle factor I’d examine is to see if content material is being lazy loaded. Refer again to the “Examine if Google sees your content material” part above. These sorts of setups have precipitated issues with the content material being picked up appropriately.

Infinite scroll points

You probably have an infinite scroll setup, I nonetheless suggest a paginated web page model in order that Google can nonetheless crawl correctly.

One other concern I’ve seen with this setup is, often, two pages get listed as one. I’ve seen this a couple of instances when individuals mentioned they couldn’t get their web page listed. However I’ve discovered their content material listed as a part of one other web page that’s often the earlier submit from them.

My concept is that when Google resized the viewport to be longer (extra on this later), it triggered the infinite scroll and loaded one other article in when it was rendering. On this case, what I like to recommend is to dam the JavaScript file that handles the infinite scrolling so the performance can’t set off.

Efficiency points

A number of the JavaScript frameworks deal with a ton of contemporary efficiency optimization for you.

All the conventional efficiency greatest practices nonetheless apply, however you get some fancy new choices. Code splitting chunks the recordsdata into smaller recordsdata. Tree shaking breaks out wanted elements, so that you’re not loading all the things for each web page such as you’d see in conventional monolithic setups. 

JavaScript setups completed effectively are a factor of magnificence. JavaScript setups that aren’t completed effectively will be bloated and trigger lengthy load instances.

Try our Core Net Vitals information for extra about web site efficiency.

JavaScript websites use extra crawl price range 

JavaScript XHR requests eat crawl price range, and I imply they gobble it down. In contrast to most different assets which can be cached, these get fetched stay in the course of the rendering course of.

One other fascinating element is that the rendering service tries to not fetch assets that don’t contribute to the content material of the web page. If it will get this mistaken, chances are you’ll be lacking some content material.

Staff aren’t supported, or are they?

Whereas Google traditionally says that it rejects service staff and repair staff can’t edit the DOM, Google’s personal Martin Splitt indicated that you could be get away with utilizing internet staff typically.

Use HTTP connections

Googlebot helps HTTP requests however doesn’t assist different connection sorts like WebSockets or WebRTC. Should you’re utilizing these, present a fallback that makes use of HTTP connections.

JavaScript website positioning testing instruments and troubleshooting

One “gotcha” with JavaScript websites is they will do partial updates of the DOM. Shopping to a different web page as a person might not replace some points like title tags or canonical tags within the DOM, however this will not be a problem for serps.

Google masses every web page stateless prefer it’s a recent load. It’s not saving earlier info and never navigating between pages.

I’ve seen SEOs get tripped up considering there’s a downside due to what they see after navigating from one web page to a different, corresponding to a canonical tag that doesn’t replace. However Google might by no means see this state.

Devs can repair this by updating the state utilizing what’s referred to as the Historical past API. However once more, it will not be an issue. A number of time, it’s simply SEOs making bother for the builders as a result of it appears bizarre to them. Refresh the web page and see what you see. Or higher but, run it by way of considered one of Google’s testing instruments to see what it sees.

Talking of its testing instruments, let’s speak about these.

Google testing instruments

Google has a number of testing instruments which can be helpful for JavaScript.

URL Inspection instrument in Google Search Console

This must be your supply of reality. If you examine a URL, you’ll get loads of information about what Google noticed and the precise rendered HTML from its system.

Using URL Inspection tool to see what Google sees after it processes JavaScript

You might have the choice to run a stay check as effectively. 

"Test Live URL" option in Google Search Console

There are some variations between the primary renderer and the stay check. The renderer makes use of cached assets and is pretty affected person. The stay check and different testing instruments use stay assets, they usually minimize off rendering early since you’re ready for a outcome. I’ll go into extra element about this within the rendering part later.

The screenshots in these instruments additionally present pages with the pixels painted, which Google doesn’t really do when rendering a web page.

The instruments are helpful to see if content material is DOM-loaded. The HTML proven in these instruments is the rendered DOM. You’ll be able to seek for a snippet of textual content to see if it was loaded in by default.

Searching for text within the DOM to make sure it's loaded by default on JavaScript sites

The instruments may also present you assets which may be blocked and console error messages, that are helpful for debugging.

Should you don’t have entry to the Google Search Console property for a web site, you’ll be able to nonetheless run a stay check on it. Should you add a redirect by yourself web site on a property the place you’ve Google Search Console entry, then you’ll be able to examine that URL and the inspection instrument will observe the redirect and present you the stay check outcome for the web page on the opposite area. 

Within the screenshot beneath, I added a redirect from my website to Google’s homepage. The stay check for this follows the redirect and exhibits me Google’s homepage. I don’t even have entry to Google’s Google Search Console account, though I want I did.

A hack to test a URL on a website you don't own

Wealthy Outcomes Check instrument

The Wealthy Outcomes Check instrument permits you to examine your rendered web page as Googlebot would see it for cellular or for desktop.

Cellular-Pleasant Check instrument

You’ll be able to nonetheless use the Cellular-Pleasant Check instrument for now, however Google has introduced it’s shutting down in December 2023.

It has the identical quirks as the opposite testing instruments from Google.


Ahrefs is the one main website positioning instrument that renders webpages when crawling the net, so we have now knowledge from JavaScript websites that no different instrument does. We render ~200M pages a day, however that’s a fraction of what we crawl.

It permits us to examine for JavaScript redirects. We are able to additionally present hyperlinks we discovered inserted with JavaScript, which we present with a JS tag within the hyperlink reviews:

Links added with JavaScript in Ahrefs' Site Explorer

Within the drop-down menu for pages in Web site Explorer, we even have an examine choice that permits you to see the historical past of a web page and examine it to different crawls. We’ve a JS marker there for pages that have been rendered with JavaScript enabled.

Pages crawled with JavaScript rendering in Ahrefs' Site Explorer

You’ll be able to allow JavaScript in Web site Audit crawls to unlock extra knowledge in your audits.

Enabling JavaScript rendering in Ahrefs' Site Audit

You probably have JavaScript rendering enabled, we are going to present the uncooked and rendered HTML for each web page. Use the “magnifying glass” choice subsequent to a web page in Web page Explorer and go to “View supply” within the menu. It’s also possible to examine towards earlier crawls and search throughout the uncooked or rendered HTML throughout all pages on the website.

Checking raw and JavaScript-rendered HTML in Ahrefs' Site Audit

Should you run a crawl with out JavaScript after which one other one with it, you should use our crawl comparability options to see variations between the variations.

Seeing changes between crawls in Ahrefs' Site Audit

Ahrefs’ website positioning Toolbar additionally helps JavaScript and permits you to examine HTML to rendered variations of tags.

Ahrefs' SEO Toolbar shows differences between raw and rendered tags like title, description, canonical

View supply vs. examine

If you right-click in a browser window, you’ll see a few choices for viewing the supply code of the web page and for inspecting the web page. View supply goes to point out you an identical as a GET request would. That is the uncooked HTML of the web page.

Use "Inspect" over "View page source" when troubleshooting JavaScript SEO issues

Examine exhibits you the processed DOM after modifications have been made and is nearer to the content material that Googlebot sees. It’s the web page after JavaScript has run and made modifications to it.

It is best to principally use examine over view supply when working with JavaScript.

Generally you’ll want to examine view supply

As a result of Google appears at each uncooked and rendered HTML for some points, you should still must examine view supply at instances. For example, if Google’s instruments are telling you the web page is marked noindex, however you don’t see a noindex tag within the rendered HTML, it’s attainable that it was there within the uncooked HTML and overwritten.

For issues like noindex, nofollow, and canonical tags, chances are you’ll must examine the uncooked HTML since points can carry over. Do not forget that Google will take essentially the most restrictive statements it noticed for the meta robots tags, and it’ll ignore canonical tags while you present it a number of canonical tags.

Don’t browse with JavaScript turned off

I’ve seen this beneficial method too many instances. Google renders JavaScript, so what you see with out JavaScript is under no circumstances like what Google sees. That is simply foolish.

Don’t use Google Cache

Google’s cache is just not a dependable approach to examine what Googlebot sees. What you usually see within the cache is the uncooked HTML snapshot. Your browser then fires the JavaScript that’s referenced within the HTML. It’s not what Google noticed when it rendered the web page.

To complicate this additional, web sites might have their Cross-Origin Useful resource Sharing (CORS) coverage arrange in a method that the required assets can’t be loaded from a distinct area.

The cache is hosted on When that area tries to request the assets from the precise area, the CORS coverage says, “Nope, you’ll be able to’t entry my recordsdata.” Then the recordsdata aren’t loaded, and the web page appears damaged within the cache.

The cache system was made to see the content material when a web site is down. It’s not notably helpful as a debug instrument.


How Google processes pages with JavaScript

Within the early days of serps, a downloaded HTML response was sufficient to see the content material of most pages. Due to the rise of JavaScript, serps now must render many pages as a browser would to allow them to see content material as how a person sees it.

The system that handles the rendering course of at Google is named the Net Rendering Service (WRS). Google has supplied a simplistic diagram to cowl how this course of works.

Googlebot crawl render and indexing process diagram
Supply: Google.

Let’s say we begin the method at URL.

1. Crawler

The crawler sends GET requests to the server. The server responds with headers and the contents of the file, which then will get saved. The headers and the content material usually are available the identical request.

The request is more likely to come from a cellular user-agent since Google is on mobile-first indexing now, but it surely additionally nonetheless crawls with the desktop user-agent. 

The requests principally come from Mountain View (CA, U.S.), but it surely additionally does some crawling for locale-adaptive pages outdoors of the U.S. As I discussed earlier, this could trigger points if websites are blocking or treating guests in a selected nation in several methods.

It’s additionally essential to notice that whereas Google states the output of the crawling course of as “HTML” on the picture above, in actuality, it’s crawling and storing the assets wanted to construct the web page just like the HTML, JavaScript recordsdata, and CSS recordsdata. There’s additionally a 15 MB max measurement restrict for HTML recordsdata.

2. Processing

There are loads of programs obfuscated by the time period “Processing” within the picture. I’m going to cowl a couple of of those which can be related to JavaScript.

Assets and hyperlinks

Google doesn’t navigate from web page to web page as a person would. A part of “Processing” is to examine the web page for hyperlinks to different pages and recordsdata wanted to construct the web page. These hyperlinks are pulled out and added to the crawl queue, which is what Google is utilizing to prioritize and schedule crawling.

Illustration showing Googlebot doesn't navigate like users

Google will pull useful resource hyperlinks (CSS, JS, and so on.) wanted to construct a web page from issues like <hyperlink> tags.

As I discussed earlier, inside hyperlinks added with JavaScript won’t get picked up till after rendering. That must be comparatively fast and never a trigger for concern usually. Issues like information websites will be the exception the place each second counts.


Each file that Google downloads, together with HTML pages, JavaScript recordsdata, CSS recordsdata, and so on., goes to be aggressively cached. Google will ignore your cache timings and fetch a brand new copy when it needs to. I’ll discuss a bit extra about this and why it’s essential within the “Renderer” part.

Illustration showing Google caches pages and resources

Duplicate elimination

Duplicate content material could also be eradicated or deprioritized from the downloaded HTML earlier than it will get despatched to rendering. I already talked about this within the “Duplicate content material” part above.

Most restrictive directives

As I discussed earlier, Google will select essentially the most restrictive statements between HTML and the rendered model of a web page. If JavaScript modifications an announcement and that conflicts with the assertion from HTML, Google will merely obey whichever is essentially the most restrictive. Noindex will override index, and noindex in HTML will skip rendering altogether.

3. Render queue

One of many largest issues from many SEOs with JavaScript and two-stage indexing (HTML then rendered web page) is that pages might not get rendered for days and even weeks. When Google appeared into this, it discovered pages went to the renderer at a median time of 5 seconds, and the ninetieth percentile was minutes. So the period of time between getting the HTML and rendering the pages shouldn’t be a priority in most instances.

Nonetheless, Google doesn’t render all pages. Like I discussed beforehand, a web page with a robots meta tag or header containing a noindex tag won’t be despatched to the renderer. It gained’t waste assets rendering a web page it may’t index anyway.

It additionally has high quality checks on this course of. If it appears on the HTML or can moderately decide from different alerts or patterns {that a} web page isn’t adequate high quality to index, then it gained’t hassle sending that to the renderer.

There’s additionally a quirk with information websites. Google needs to index pages on information websites quick so it may index the pages based mostly on the HTML content material first—and are available again later to render these pages.

4. Renderer

The renderer is the place Google renders a web page to see what a person sees. That is the place it’s going to course of the JavaScript and any modifications made by JavaScript to the DOM.

Illustration of how JavaScript can change the DOM

For this, Google is utilizing a headless Chrome browser that’s now “evergreen,” which implies it ought to use the most recent Chrome model and assist the most recent options. Years in the past, Google was rendering with Chrome 41, and plenty of options weren’t supported at that time.

Google has extra information on the WRS, which incorporates issues like denying permissions, being stateless, flattening mild DOM and shadow DOM, and extra that’s value studying.

Rendering at web-scale will be the eighth surprise of the world. It’s a severe endeavor and takes an amazing quantity of assets. Due to the dimensions, Google is taking many shortcuts with the rendering course of to hurry issues up.

Cached assets

Google is relying closely on caching assets. Pages are cached. Recordsdata are cached. Almost all the things is cached earlier than being despatched to the renderer. It’s not going out and downloading every useful resource for each web page load, as a result of that may be costly for it and web site homeowners. As an alternative, it makes use of these cached assets to be extra environment friendly.

The exception to that’s XHR requests, which the renderer will do in actual time.

There’s no five-second timeout

A typical website positioning fantasy is that Google solely waits 5 seconds to load your web page. Whereas it’s at all times a good suggestion to make your website quicker, this fantasy doesn’t actually make sense with the best way Google caches recordsdata talked about above. It’s already loading a web page with all the things cached in its programs, not making requests for recent assets.

Illustration of how resources from the page and file cache are sent to the WRS for rendering

If it solely waited 5 seconds, it might miss loads of content material.

The parable doubtless comes from the testing instruments just like the URL Inspection instrument the place assets are fetched stay as an alternative of cached, and they should return a outcome to customers inside an inexpensive period of time. It might additionally come from pages not being prioritized for crawling, which makes individuals suppose they’re ready a very long time to render and index them.

There is no such thing as a mounted timeout for the renderer. It runs with a sped-up timer to see if something is added at a later time. It additionally appears on the occasion loop within the browser to see when all the actions have been taken. It’s actually affected person, and also you shouldn’t be involved about any particular time restrict.

It’s affected person, but it surely additionally has safeguards in place in case one thing will get caught or somebody is making an attempt to mine Bitcoin on its pages. Sure, it’s a factor. We had so as to add safeguards for Bitcoin mining as effectively and even printed a research about it.

What Googlebot sees

Googlebot doesn’t take motion on webpages. It’s not going to click on issues or scroll, however that doesn’t imply it doesn’t have workarounds. So long as content material is loaded within the DOM and not using a wanted motion, Google will see it. If it’s not loaded into the DOM till after a click on, then the content material gained’t be discovered.

Google doesn’t must scroll to see your content material both as a result of it has a intelligent workaround to see the content material. For cellular, it masses the web page with a display measurement of 411×731 pixels and resizes the size to 12,140 pixels

Basically, it turns into a very lengthy cellphone with a display measurement of 411×12140 pixels. For desktop, it does the identical and goes from 1024×768 pixels to 1024×9307 pixels. I haven’t seen any latest assessments for these numbers, and it might change relying on how lengthy the pages are.

Illustration showing Google doesn't scroll to see content

One other fascinating shortcut is that Google doesn’t paint the pixels in the course of the rendering course of. It takes time and extra assets to complete a web page load, and it doesn’t actually need to see the ultimate state with the pixels painted. Apart from, graphics playing cards are costly between gaming, crypto mining, and AI.

Google simply must know the construction and the structure, and it will get that with out having to really paint the pixels. As Martin places it:

In Google search we don’t actually care concerning the pixels as a result of we don’t actually need to present it to somebody. We need to course of the knowledge and the semantic info so we’d like one thing within the intermediate state. We don’t have to really paint the pixels.

A visible might assist clarify what’s minimize out a bit higher. In Chrome Dev Instruments, in the event you run a check on the “Efficiency” tab, you get a loading chart. The strong inexperienced half right here represents the portray stage. For Googlebot, that by no means occurs, so it saves assets.

Performance chart from Chrome Dev Tools

Grey = Downloads
Blue = HTML
Yellow = JavaScript
Purple = Format
Inexperienced = Portray

5. Crawl queue

Google has a useful resource that talks a bit about crawl price range. However it’s best to know that every website has its personal crawl price range, and every request must be prioritized. Google additionally has to stability crawling your pages vs. each different web page on the web.

Newer websites usually or websites with loads of dynamic pages will doubtless be crawled slower. Some pages might be up to date much less usually than others, and a few assets might also be requested much less steadily.


JavaScript rendering choices

There are many choices with regards to rendering JavaScript. Google has a strong chart that I’m simply going to point out. Any form of SSR, static rendering, and prerendering setup goes to be superb for serps. Gatsby, Subsequent, Nuxt, and so on., are all nice.

JavaScript rendering options

Probably the most problematic one goes to be full client-side rendering the place all the rendering occurs within the browser. Whereas Google will in all probability be OK client-side rendering, it’s greatest to decide on a distinct rendering choice to assist different serps.

Bing additionally has assist for JavaScript rendering, however the scale is unknown. Yandex and Baidu have restricted assist from what I’ve seen, and plenty of different serps have little to no assist for JavaScript. Our personal search engine, Yep, has assist, and we render ~200M pages per day. However we don’t render each web page we crawl.

There’s additionally the choice of dynamic rendering, which is rendering for sure user-agents. It is a workaround and, to be sincere, I by no means beneficial it and am glad Google is recommending towards it now as effectively.

Situationally, chances are you’ll need to use it to render for sure bots like serps and even social media bots. Social media bots don’t run JavaScript, so issues like OG tags gained’t be seen except you render the content material earlier than serving it to them.

Virtually, it makes setups extra advanced and tougher for SEOs to troubleshoot. It’s positively cloaking, although Google says it’s not and that it’s OK with it.


Should you have been utilizing the previous AJAX crawling scheme with hashbangs (#!), do know this has been deprecated and is not supported.

Ultimate ideas

JavaScript is just not one thing for SEOs to concern. Hopefully, this text has helped you perceive tips on how to work with it higher. 

Don’t be afraid to achieve out to your builders and work with them and ask them questions. They’ll be your biggest allies in serving to to enhance your JavaScript website for serps.

Have questions? Let me know on Twitter.

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