how to fix render blocking javascript and css?

JavaScript and CSS rendering present real problems for web performance optimization, but these issues generally affect the user experience and the webpage load times. Render-blocking resources make the browser wait until above-the-fold resources (the portion of a webpage visible without scrolling) have been completely loaded and processed. The consequence of this is in effect that it induces such irritation which leads to the customers leaving the website without purchase.

JavaScript and CSS rendering blocking in the elements of above-the-fold content is of utmost importance for Web developers to achieve seamless rendering and the fastest load time. Step by step this tutorial will provide guidance and a definition of what you can do to hit the spot with keywords.

- Pinpoint render-blocking resources Firstly, you should spot which CSS and JavaScript files are slowing down or completely preventing the content above the fold from being visible. By using different tools you can eliminate your website’s troublesome pages and propose the appropriate fix measures:

- Google PageSpeed Insights: This free tool for Google can analyze your website, which gives you recommendations and even sign-posts of resources that when blocked can hinder your rendering.

- WebPageTest: The web service enables you to apply performance tests to your site's page and then if you get waterfall charts that describe the date when resources are slow or inhibiting the rendering.

- Chrome DevTools: In the DevTools menu in Chrome browser(F12 on nix or Ctrl+Shift+I on Mac or Cmd+Option+I on Mac), select the "Network" tab and check the file marked as "Blocking" or "Parser Blocking" resource.

- Crunching and even shrinking web page CSS and JavaScript files can significantly speed up the page download and parsing process due to the fact the data file size is greatly reduced. Minification eliminates the whitespaces, inline code, and passing comments, on the other hand, Brotli or Gzip compression damages much smaller files for transmission.

You can code minify and compress your files manually or use build tools such as Grunt, Gulp, or Webpack which automate this. Besides, enabled by default from many content delivery networks (CDN) and web servers they can automatically compress files for you.

- Inline Critical CSS: Critical CSS used here means, CSS that is a minimum required to display the above-the-fold content of a web page. Time is of critical value, therefore, including important CSS inline gives you the benefit of allowing a browser to complete showing the visible part without waiting for external CSS files to download.

Can use tools such as Critical Path CSS, which extracts the critical CSS by analyzing your web pages to fraudulently identify and inline critical CSS. However, another alternative option is going for sites like UnCSS or PurifyCSS which help to look through your stylesheets and cut away the unnecessary CSS, resulting in a lighter size of your stylesheets and a higher speed performance.

- Consider Deferring Non-Critical CSS: The main takeaway of this article is that inline critical styles while deferring non-critical files until after the initial render is the best choice. This ensures that creating a fast loading of above-the-fold content which is displayed quickly without any delay, but the rest of the CSS styles are loaded asynchronously.

To postpone non-urgent CSS execution, you can use the "rel="preload" resource hint within your HTML to inform the browser to load the non-urgent CSS files even after the initial render has happened, or you can use JavaScript to dynamically load the CSS files when the page is completely loaded.

- Postponing Render-blocking JavaScript Just as with non-critical CSS, any JavaScript that is not needed for the render and loading process of the above-the-fold content should be delayed from execution until such a time that the main content is already displayed. This is the case when none of the above is required for the core functionality.

To put off large scripts that could render-block the execution, you can do this by giving async or defer attributes to JavaScript tags, or by loading the scripts using JavaScript after page loading. Moreover, these asynchronous loading techniques incorporate a load of JavaScript code by either code splitting, or lazy loading that loads script only when needed.

- Optimize the Third-Party Scripts When optimizing third-party scripts like these, which are for advertisement, analysis, or social media integration, can block rendering and prolong load times. This problem could be overcome by putting measures in place such as:

- Look for and stake out all insignificant third-party scripts.

- Make third-party scripts work asynchronously through the attribute such as async or dynamic loading.

- Otherwise, host the libraries yourself or use a CDN instead of fetching them from other sites thus reducing download duration.

- Instruction HTTP/2 and perform top Server PUSH HTTP/2 is the most recent version of HTTP protocol that provides an array of improvements compared to its predecessor, HTTP/1.1. One of the major characteristics of HTTP/2 is the server push which can push previously requested assets (CSS, images, JavaScript) from the server to the client even before the client reaches for them.

The function of the HTTP/2 protocol as well as the server push technique enables the situation of the render-blocking resources not to happen anymore. Through the server’s ability to push the imperative CSS and Javascript goods to get the fold section to look appropriately on page load.

- Continuous Checking and Tuning a website’s performance is one such task because newer resources, technologies, and practices are being introduced all the time. We should not ignore the fact that incessant monitoring of the website’s performance and rendering of the blockages is critical.

Instruments/Tools such as WebPageTest, Google PageSpeed Insights, and Chrome dev tools can you help you navigate, and identify various performance bottlenecks. Besides that always maintain a continuous integration and deployment (CI/CD) process that can optimize your website both in the development stage and during deployment for the best results.

With these easy-to-use steps, you will be able to boost your site performance as far as rendering goes and it won't matter much whether your users will stay a short or a long time on your website. Doing without render-blocking JavaScript and CSS in the top-matter content is eminently of web performance optimization and can bring the engagement, conversion levels, and rankings of search engines certainly down.

However, the optimization of web performance is an ongoing process and requires keeping track of changing demands, testing, and making adjustments if necessary to ensure that your website is always fast and responsive as new technologies and best practices like the ones mentioned above are introduced.