The Definitive Guide to JavaScript SEO (2021 Edition)

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The net is in a golden age of front-end growth, and JavaScript and technical SEO are experiencing a renaissance. As a technical SEO specialist and net dev fanatic at an award-winning digital advertising and marketing company, I’d like to share my perspective on fashionable JavaScript SEO primarily based on trade finest practices and my very own company expertise. In this text, you will learn the way to optimize your JS-powered web site for search in 2021.

What is JavaScript SEO?

JavaScript SEO is the self-discipline of technical SEO that’s targeted on optimizing web sites constructed with JavaScript for visibility by engines like google. It’s primarily involved with:

  • Optimizing content material injected through JavaScript for crawling, rendering, and indexing by engines like google.
  • Preventing, diagnosing, and troubleshooting rating points for web sites and SPAs (Single Page Applications) constructed on JavaScript frameworks, equivalent to React, Angular, and Vue.
  • Ensuring that net pages are discoverable by engines like google by linking finest practices.
  • Improving web page load occasions for pages parsing and executing JS code for a streamlined User Experience (UX).

 Is JavaScript good or unhealthy for SEO?

It relies upon! JavaScript is crucial to the trendy net and makes constructing web sites scalable and simpler to preserve. However, sure implementations of JavaScript may be detrimental to search engine visibility.

How does JavaScript have an effect on SEO?

JavaScript can have an effect on the next on-page parts and rating components which might be vital for SEO:

  • Rendered content material
  • Links
  • Lazy-loaded pictures
  • Page load occasions
  • Meta information

What are JavaScript-powered web sites?

When we discuss websites which might be constructed on JavaScript, we’re not referring to merely including a layer of JS interactivity to HTML paperwork (for instance, when including JS animations to a static net web page). In this case, JavaScript-powered web sites refer to when the core or major content material is injected into the DOM through JavaScript.

App Shell Model.

This template known as an app shell and is the inspiration for progressive net functions (PWAs). We’ll discover this subsequent.

How to examine if a web site is constructed with JavaScript

You can shortly examine if a web site is constructed on a JavaScript framework through the use of a expertise look-up instrument equivalent to BuiltWith or Wappalyzer. You may “Inspect Element” or “View Source” within the browser to examine for JS code. Popular JavaScript frameworks that you simply would possibly discover embody:

JavaScript SEO for core content material

Here’s an instance: Modern net apps are being constructed on JavaScript frameworks, like Angular, React, and Vue. JavaScript frameworks enable builders to shortly construct and scale interactive net functions. Let’s check out the default venture template for Angular.js, a well-liked framework produced by Google.

When seen within the browser, this seems like a typical net web page. We can see textual content, pictures, and hyperlinks. However, let’s dive deeper and take a peek underneath the hood on the code:

Now we are able to see that this HTML doc is nearly fully devoid of any content material. There are solely the app-root and some script tags within the physique of the web page. This is as a result of the principle content material of this single web page utility is dynamically injected into the DOM through JavaScript. In different phrases, this app is determined by JS to load key on-page content material!

Potential SEO points: Any core content material that’s rendered to customers however not to search engine bots might be significantly problematic! If engines like google aren’t in a position to totally crawl your entire content material, then your web site might be neglected in favor of opponents. We’ll talk about this in additional element later.

JavaScript SEO for inner hyperlinks

Besides dynamically injecting content material into the DOM, JavaScript may have an effect on the crawlability of hyperlinks. Google discovers new pages by crawling hyperlinks it finds on pages.

As a finest observe, Google particularly recommends linking pages utilizing HTML anchor tags with href attributes, in addition to together with descriptive anchor texts for the hyperlinks:

However, Google additionally recommends that builders not depend on different HTML parts — like div or span — or JS occasion handlers for hyperlinks. These are referred to as “pseudo” hyperlinks, and they’ll usually not be crawled, in accordance to official Google pointers:

Despite these pointers, an unbiased, third-party examine has instructed that Googlebot could have the option to crawl JavaScript hyperlinks. Nonetheless, in my expertise, I’ve discovered that it’s a finest observe to preserve hyperlinks as static HTML parts.

Potential SEO points: If engines like google aren’t in a position to crawl and observe hyperlinks to your key pages, then your pages might be lacking out on useful inner hyperlinks pointing to them. Internal hyperlinks assist engines like google crawl your web site extra effectively and spotlight crucial pages. The worst-case situation is that in case your inner hyperlinks are applied incorrectly, then Google could have a tough time discovering your new pages in any respect (exterior of the XML sitemap).

JavaScript SEO for lazy-loading pictures

JavaScript may have an effect on the crawlability of pictures which might be lazy-loaded. Here’s a fundamental instance. This code snippet is for lazy-loading pictures within the DOM through JavaScript:

Googlebot helps lazy-loading, but it surely doesn’t “scroll” like a human consumer would when visiting your net pages. Instead, Googlebot merely resizes its digital viewport to be longer when crawling net content material. Therefore, the “scroll” occasion listener isn’t triggered and the content material isn’t rendered by the crawler.

Here’s an instance of extra SEO-friendly code:

This code exhibits that the IntersectionObserver API triggers a callback when any noticed component turns into seen. It’s extra versatile and sturdy than the on-scroll occasion listener and is supported by fashionable Googlebot. This code works due to how Googlebot resizes its viewport so as to “see” your content material (see under).

You may use native lazy-loading within the browser. This is supported by Google Chrome, however word that it’s nonetheless an experimental function. Worst case situation, it can simply get ignored by Googlebot, and all pictures will load anyway:

Native lazy-loading in Google Chrome.

Potential SEO points: Similar to core content material not being loaded, it’s vital to be sure that Google is in a position to “see” the entire content material on a web page, together with pictures. For instance, on an e-commerce web site with a number of rows of product listings, lazy-loading pictures can present a quicker consumer expertise for each customers and bots!

Javascript SEO for web page pace

Javascript may have an effect on web page load occasions, which is an official rating consider Google’s mobile-first index. This signifies that a sluggish web page might doubtlessly hurt rankings in search. How can we assist builders mitigate this?

  • Minifying JavaScript
  • Deferring non-critical JS till after the principle content material is rendered within the DOM
  • Inlining crucial JS
  • Serving JS in smaller payloads

Potential SEO points: A sluggish web site creates a poor consumer expertise for everybody, even engines like google. Google itself defers loading JavaScript to save assets, so it’s vital to be sure that any served to shoppers is coded and delivered effectively to assist safeguard rankings.

JavaScript SEO for meta information

Also, it’s vital to word that SPAs that make the most of a router bundle like react-router or vue-router have to take some additional steps to deal with issues like altering meta tags when navigating between router views. This is normally dealt with with a Node.js bundle like vue-meta or react-meta-tags.

What are router views? Here’s how linking to completely different “pages” in a Single Page Application works in React in 5 steps:

  1. When a consumer visits a React web site, a GET request is shipped to the server for the ./index.html file.
  2. The server then sends the index.html web page to the consumer, containing the scripts to launch React and React Router.
  3. The net utility is then loaded on the client-side.
  4. If a consumer clicks on a hyperlink to go on a brand new web page (/instance), a request is shipped to the server for the brand new URL.
  5. React Router intercepts the request earlier than it reaches the server and handles the change of web page itself. This is completed by regionally updating the rendered React parts and altering the URL client-side.

In different phrases, when customers or bots observe hyperlinks to URLs on a React web site, they don’t seem to be being served a number of static HTML information. But relatively, the React parts (like headers, footers, and physique content material) hosted on root ./index.html file are merely being reorganized to show completely different content material. This is why they’re referred to as Single Page Applications!

Potential SEO points: So, it’s vital to use a bundle like React Helmet for ensuring that customers are being served distinctive metadata for every web page, or “view,” when looking SPAs. Otherwise, engines like google could also be crawling the identical metadata for each web page, or worse, none in any respect!

How does this all have an effect on SEO within the greater image? Next, we want to learn the way Google processes JavaScript.

How does Google deal with JavaScript?

In order to perceive how JavaScript impacts SEO, we want to perceive what precisely occurs when GoogleBot crawls an internet web page:

  1. Crawl
  2. Render
  3. Index

First, Googlebot crawls the URLs in its queue, web page by web page. The crawler makes a GET request to the server, usually utilizing a cellular user-agent, after which the server sends the HTML doc.

Then, Google decides what assets are vital to render the principle content material of the web page. Usually, this implies solely the static HTML is crawled, and never any linked CSS or JS information. Why?

According to Google Webmasters, Googlebot has found roughly 130 trillion net pages. Rendering JavaScript at scale may be expensive. The sheer computing energy required to obtain, parse, and execute JavaScript in bulk is huge.

This is why Google could defer rendering JavaScript till later. Any unexecuted assets are queued to be processed by Google Web Rendering Services (WRS), as computing assets change into accessible.

Finally, Google will index any rendered HTML after JavaScript is executed.

Google crawl, render, and index course of.

In different phrases, Google crawls and indexes content material in two waves:

  1. The first wave of indexing, or the moment crawling of the static HTML despatched by the webserver
  2. The second wave of indexing, or the deferred crawling of any further content material rendered through JavaScript
Google wave indexing. Source: Google I/O’18

The backside line is that content material depending on JS to be rendered can expertise a delay in crawling and indexing by Google. This used to take days and even weeks. For instance, Googlebot traditionally ran on the outdated Chrome 41 rendering engine. However, they’ve considerably improved its net crawlers lately.

Googlebot was not too long ago upgraded to the newest steady launch of the Chromium headless browser in May 2019. This signifies that their net crawler is now “evergreen” and totally suitable with ECMAScript 6 (ES6) and better, or the newest variations of JavaScript.

So, if Googlebot can technically run JavaScript now, why are we nonetheless apprehensive about indexing points?

The quick reply is crawl finances. This is the idea that Google has a fee restrict on how steadily they’ll crawl a given web site due to restricted computing assets. We already know that Google defers JavaScript to be executed later to save crawl finances.

While the delay between crawling and rendering has been decreased, there is no such thing as a assure that Google will really execute the JavaScript code ready in line in its Web Rendering Services queue.

Here are some the explanation why Google won’t really ever run your JavaScript code:

  • Blocked in robots.txt
  • Timeouts
  • Errors

Therefore, JavaScript may cause SEO points when core content material depends on JavaScript however isn’t rendered by Google.

Real-world utility: JavaScript SEO for e-commerce

E-commerce web sites are a real-life instance of dynamic content material that’s injected through JavaScript. For instance, on-line shops generally load merchandise onto class pages through JavaScript.

JavaScript can enable e-commerce web sites to replace merchandise on their class pages dynamically. This is sensible as a result of their stock is in a continuing state of flux due to gross sales. However, is Google really in a position to “see” your content material if it doesn’t execute your JS information?

For e-commerce web sites, which depend upon on-line conversions, not having their merchandise listed by Google might be disastrous.

How to take a look at and debug JavaScript SEO points

Here are steps you possibly can take at present to proactively diagnose any potential JavaScript SEO points:

  1. Visualize the web page with Google’s Webmaster Tools. This helps you to view the web page from Google’s perspective.
  2. Use the positioning search operator to examine Google’s index. Make certain that your entire JavaScript content material is being listed correctly by manually checking Google.
  3. Debug utilizing Chrome’s built-in dev instruments. Compare and distinction what Google “sees” (supply code) with what customers see (rendered code) and be sure that they align normally.

There are additionally helpful third-party instruments and plugins that you need to use. We’ll discuss these quickly.

Google Webmaster Tools

The finest method to decide if Google is experiencing technical difficulties when trying to render your pages is to take a look at your pages utilizing Google Webmaster instruments, equivalent to:

Google Mobile-Friendly Test.

The aim is just to visually evaluate and distinction your content material seen in your browser and search for any discrepancies in what’s being displayed within the instruments.

Both of those Google Webmaster instruments use the identical evergreen Chromium rendering engine as Google. This signifies that they can provide you an correct visible illustration of what Googlebot really “sees” when it crawls your web site.

There are additionally third-party technical SEO instruments, like Merkle’s fetch and render instrument. Unlike Google’s instruments, this net utility really provides customers a full-size screenshot of all the web page.

Site: Search Operator

Alternatively, if you’re not sure if JavaScript content material is being listed by Google, you possibly can carry out a fast check-up through the use of the positioning: search operator on Google.

Copy and paste any content material that you simply’re undecided that Google is indexing after the positioning: operator and your area title, after which press the return key. If you will discover your web page within the search outcomes, then no worries! Google can crawl, render, and index your content material simply tremendous. If not, it means your JavaScript content material would possibly want some assist gaining visibility.

Here’s what this seems like within the Google SERP:

Chrome Dev Tools

Another technique you need to use to take a look at and debug JavaScript SEO points is the built-in performance of the developer instruments accessible within the Chrome net browser.

Right-click anyplace on an internet web page to show the choices menu after which click on “View Source” to see the static HTML doc in a brand new tab.

You may click on “Inspect Element” after right-clicking to view the content material that’s really loaded within the DOM, together with JavaScript.

Inspect Element.

Compare and distinction these two views to see if any core content material is just loaded within the DOM, however not hard-coded within the supply. There are additionally third-party Chrome extensions that may assist do that, just like the Web Developer plugin by Chris Pederick or the View Rendered Source plugin by Jon Hogg.

How to repair JavaScript rendering points

After diagnosing a JavaScript rendering downside, how do you resolve JavaScript SEO points? The reply is easy: Universal Javascript, often known as “Isomorphic” JavaScript. 

What does this imply? Universal or Isomorphic right here refers to JavaScript functions which might be able to being run on both the server or the consumer.

There are just a few completely different implementations of JavaScript which might be extra search-friendly than client-side rendering, to keep away from offloading JS to each customers and crawlers:

  • Server-side rendering (SSR). This signifies that JS is executed on the server for every request. One method to implement SSR is with a Node.js library like Puppeteer. However, this could put loads of pressure on the server.
  • Hybrid rendering. This is a mixture of each server-side and client-side rendering. Core content material is rendered server-side earlier than being despatched to the consumer. Any further assets are offloaded to the consumer.
  • Dynamic rendering. In this workaround, the server detects the consumer agent of the consumer making the request. It can then ship pre-rendered JavaScript content material to engines like google, for instance. Any different consumer brokers will want to render their content material client-side. For instance, Google Webmasters suggest a well-liked open-source answer referred to as Renderton for implementing dynamic rendering.
  • Incremental Static Regeneration, or updating static content material after a web site has already been deployed. This may be accomplished with frameworks like Next.js for React or Nuxt.js for Vue. These frameworks have a construct course of that can pre-render each web page of your JS utility to static belongings that you would be able to serve from one thing like an S3 bucket. This method, your web site can get the entire SEO advantages of server-side rendering, with out the server administration!

Each of those options helps be sure that, when search engine bots make requests to crawl HTML paperwork, they obtain the totally rendered variations of the online pages. However, a few of these may be extraordinarily troublesome and even not possible to implement after net infrastructure is already constructed. That’s why it’s vital to preserve JavaScript SEO finest practices in thoughts when designing the structure of your subsequent net utility.

Note, for web sites constructed on a content material administration system (CMS) that already pre-renders most content material, like WordPress or Shopify, this isn’t usually a difficulty.

Key takeaways

This information gives some common finest practices and insights into JavaScript SEO. However, JavaScript SEO is a fancy and nuanced subject of examine. We suggest that you simply learn by Google’s official documentation and troubleshooting information for extra JavaScript SEO fundamentals. Interested in studying extra about optimizing your JavaScript web site for search? Leave a remark under.


Want to be taught extra about technical SEO? Check out the Moz Academy Technical SEO Certification Series, an in-depth coaching collection that hones in on the nuts and bolts of technical SEO.

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