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Defer Parsing Of Javascript: Javascript Explained

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Javascript is a powerful scripting language used to create dynamic web features and apps. As a powerful programming language, it is essential to optimize the loading speed of any javascript code within a website or web application. Defer Parsing of Javascript is an important optimization technique that can be used to improve the loading speed of your website.

What is Javascript?

Javascript is a scripting language that provides a host of features for creating user interfaces, animations and advanced functionalities. It is the only scripting language that can be used in modern web browsers. It is asynchronous, meaning that it can execute code in parallel without waiting for the response from the server. It can also be used to create single-page applications.

Javascript is a powerful language that can be used to create dynamic webpages and applications. It is also used to create interactive webpages, such as games and interactive forms. It is a popular language among web developers, as it is relatively easy to learn and use. Additionally, it is supported by all major web browsers, making it a great choice for web development.

Why is Defer Parsing of Javascript Important?

Defer Parsing of Javascript is an important optimization technique that can be implemented to reduce the loading time of your web pages. Javascript files, if they are not deferred, block the HTML parser while they are downloading and executing, preventing the rest of the web page from loading. By deferring the Javascript files, the HTML parser can continue working while the Javascript is downloaded and parsed separately.

Deferring Javascript can also help to improve the user experience of your website. By reducing the loading time of your web pages, users will be able to access the content they are looking for more quickly. Additionally, deferring Javascript can help to reduce the amount of data that needs to be downloaded, which can help to reduce the cost of hosting your website.

What Are The Benefits Of Defer Parsing Of Javascript?

Defer Parsing of Javascript can improve the speed and performance of your web page. By preventing the HTML parser from stalling while the Javascript files are being downloaded, the remaining elements on the page are able to be loaded faster. This makes your webpages feel much more responsive and reduces waiting time for users. Additionally, deferring Javascript can improve your website’s SEO rankings as search engine crawlers are better able to access your content directly.

Deferring Javascript can also help to reduce the amount of data that needs to be transferred from the server to the user’s browser. By only loading the necessary Javascript files, the amount of data that needs to be transferred is reduced, resulting in faster page loading times. Furthermore, deferring Javascript can help to reduce the amount of memory used by the browser, as the browser does not need to store the entire Javascript file in memory.

What Are The Drawbacks Of Defer Parsing Of Javascript?

Although deferring Javascript can improve loading speed and provide other performance benefits, it can also have some drawbacks. Depending on the type of application and the Javascript code within it, deferring might cause some unexpected problems. The code might not execute correctly as it was not designed to be executed on a separate thread or after the page has been loaded. In some cases, it is best to defer the loading of some Javascript and not others, making sure to test thoroughly after the changes are made.

Additionally, deferring Javascript can cause compatibility issues with older browsers. If the code is not written to be compatible with older browsers, it may not execute correctly or at all. It is important to consider the potential compatibility issues when deferring Javascript, and to test the code on multiple browsers to ensure that it is working correctly.

How To Implement Defer Parsing Of Javascript?

It is important to remember that deferring parsing of Javascript requires careful implementation to make sure that everything works properly. The easiest way to implement deferring is by adding the “defer” attribute to all Javascript files in the head of your HTML document. This way, all files are loaded asynchronously and in parallel, without blocking the HTML parser.

It is also important to note that deferring parsing of Javascript can have a negative impact on the performance of your website. This is because the browser must wait for the Javascript to be parsed before it can render the page. Therefore, it is important to ensure that the Javascript is optimized and that the code is as efficient as possible.

When Should You Avoid Defer Parsing Of Javascript?

While deferring parsing of Javascript can bring many performance benefits to your website or application, there are certain cases in which deferring should be avoided. If your Javascript code needs to be executed immediately after the page load, deferring it will not offer any performance benefits and could even break the code. Additionally, if your code contains any errors that would prevent it from executing properly, deferring it could cause some unexpected problems and should be avoided until these errors are fixed.

It is also important to note that deferring parsing of Javascript can cause issues with certain third-party scripts, such as analytics and tracking scripts. If you are using any third-party scripts, it is best to test the performance of your website or application both with and without deferring parsing of Javascript to ensure that it does not cause any unexpected issues.

Conclusion

Defer Parsing of Javascript is an important optimization technique that can help improve the loading speed of your webpages and web applications. By preventing the HTML parser from stalling while waiting for Javascript files to be downloaded and execute, it can make your website feel much faster and responsive while also improving your SEO rankings in search engine queries. While there are some cases in which deferring should be avoided, such as when Javascript needs to be executed immediately after page load or when it contains errors, it can provide many performance advantages when implemented correctly.

In addition to improving page loading speed, deferring parsing of Javascript can also help reduce the amount of data that needs to be transferred over the network. By deferring the loading of Javascript files until they are needed, you can reduce the amount of data that needs to be sent to the user’s browser, resulting in a faster and more efficient loading experience.

Sarang Sharma

Sarang Sharma

Sarang Sharma is Software Engineer at Bito with a robust background in distributed systems, chatbots, large language models (LLMs), and SaaS technologies. With over six years of experience, Sarang has demonstrated expertise as a lead software engineer and backend engineer, primarily focusing on software infrastructure and design. Before joining Bito, he significantly contributed to Engati, where he played a pivotal role in enhancing and developing advanced software solutions. His career began with foundational experiences as an intern, including a notable project at the Indian Institute of Technology, Delhi, to develop an assistive website for the visually challenged.

Written by developers for developers

This article was handcrafted with by the Bito team.

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