What is render blocking?

What is render blocking?

Overview. Render-blocking resources are scripts, stylesheets, and HTML imports that block or delay the browser from rendering page content to the screen. These resources delay the First Paint – the time at which your browser renders something (i.e., background colours, borders, text or images) for the first time.

How do I fix render blocking?

To reduce the number of render-blocking scripts on your site, you’ll need to follow a few best practices:

1. ‘Minify’ your JavaScript and CSS. This means removing all extra whitespace and unnecessary comments in the code.
2. Concatenate your JavaScript and CSS.
3. Defer the loading of JavaScript.

What is render blocking code?

Simply put, JavaScript is a piece of code that might be present on your website to enable some functions of your theme or plugins. And “Render Blocking” means that these JavaScript codes are either blocking, or slowing down how your website is displayed, or rendered, by your browser.

Are images render blocking?

Remember, images aren’t render blocking so if you have images on the blue DOM line you can safely ignore those; although you will still want to optimize your images. While HTML is also a render blocking resource, the DOM can be built incrementally.

Is Async render blocking?

Async specifies that scripts can load asynchronously without causing render-blocking as the browser reads the HTML document — and execute as soon as they’ve finished loading.

How do I eliminate render blocking resources?

There are three ways to reduce the number and impact of render blocking resources:

1. Make them non-render blocking resources by deferring their download.
2. Decrease the total number of render blocking resources using techniques such as bundling (this also means fewer HTTP requests)

What causes render blocking?

Render blocking resources are static files, such as fonts, HTML, CSS, and JavaScript files, that are vital to the process of rendering a web page. When the browser encounters a render blocking resource, it stops downloading the rest of the resources until these critical files are processed.

How can I eliminate render blocking resources?

Now let’s zoom in on five strategies to eliminate or reduce the number and impact of render blocking resources.

1. Don’t add CSS with the @import rule.
2. Use the media attribute for conditional CSS.
3. Use the defer and async attributes to eliminate render blocking JavaScript.
4. Minify and bundle CSS and JavaScript.

What does it mean to use render blocking resources?

Render-blocking resources are files that “press pause” on the critical rendering path. They interrupt one or more of the steps. HTML is technically render blocking because you need it to create the DOM. Without the HTML we would not even have a page to render.

When to use CSS as a render blocker?

The browser blocks rendering until it has both the DOM and the CSSOM. CSS is a render blocking resource. Get it to the client as soon and as quickly as possible to optimize the time to first render.

How to get rid of render blocking JavaScript?

To find out where the scripts and stylesheets that are render-blocking are located, go to the Google Page Speed Insights Tool and analyze your website. Then, look at the suggestions tab and find the section that reads: Eliminate render-blocking JavaScript and CSS in above-the-fold content.

How to unblock the rendering path in CSS?

Make sure to keep your CSS lean, deliver it as quickly as possible, and use media types and queries to unblock rendering. In the render tree construction we saw that the critical rendering path requires both the DOM and the CSSOM to construct the render tree.