What do we mean by the main thread?
The main thread is where the browser handles most of the work involved in page loadings, such as rendering/painting content and handling user interaction.
On the main thread, the browser performs the following tasks:
- Layout management
- Parsing CSS and HTML
- Building the Document Object Model (DOM)
They were thinking of the main thread as a butler in a hotel for a while. The butler must take orders, deliver food, refill drinks, handle payment, etc. If the butler gets slowed down while compiling a single order only, e.g., customers are indecisive or have a complicated order), the butler cannot process other orders.
This creates a bottleneck, which affects our perception of the hotel's performance.
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What is the impact of minimizing main thread work on our page's performance?
When we minimize the main thread's activity, the browser has more room to focus on the other critical activities of page loading.
Returning to our butler scenario, the fewer the tasks he has to complete, the faster he can deliver service. As a consequence, the hotel's whole experience will be enhanced.
How to minimize the main thread work?
One of the most critical goals in your development workflow should be Minimizing main-thread work.
- It reduces the time spent evaluating scripts.
- Minimizing style and layout recalculations.
- Preventing the delay in rendering page pixels: Compress any remaining critical resources to save space.
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Top 3 ways to reduce the main thread work
The Prominent ways to reduce the main thread work are described below:
Optimize Third-Party Code
We should evaluate the third-party code on our website and eliminate those that aren't adding value to it.
Delay non-essential scripts, create early connections to critical third-party sites, lazy-load embedded third-party material, and optimize third-party hosting to improve other scripts.
Uses of web workers
The main thread has more to accomplish as the features and functionality of web programs get more complex, increasing the likelihood of bottlenecks. Furthermore, because each device has varied capabilities, it is nearly difficult to forecast how long it will take to run the code on the main thread.
Executing code off the main thread (OMT) using Web workers that run alongside the main thread is a workaround for this problem. Web workers facilitate parallel processing by allowing you to assign a function to a thread that runs in parallel with the rest of your program. When we code Without a web worker, for example. When we code with web worker, for example
Minify and defer CSS
You must download and parse the CSS file before the browser can display the page. Larger CSS files can clog the main thread for a long time and slow down the time it takes to load the page and respond to user actions.
CSS files may contain unwanted characters, comments, spaces, or tabs. Removing these unwanted characters will reduce the final size without affecting how the browser displays the style. This process is called depreciation and helps reduce the work of the main thread. However, creating CSS code without these characters is unnatural and difficult.
Defer non-critical CSS
It's important to understand that CSS files are render-blocking resources. You must load the CSS file before the browser starts the dialogue on the main thread. This means that the big style gives more work to the main thread. Fortunately, not all lines of CSS are needed to create important content. DevTools coverage tools show important CSS classes for loading pages. Extract critical CSS from the coverage tool and load it into the block at the top of the page. Then you can load unimportant classes asynchronously. This reduces the work of the main thread.
This makes the page interactive and significantly reduces loading time. Not only does this improve your Lighthouse score, but it also reduces the bounce rate and spends more time on it because users don't have to wait for the page to be used.
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- Begin by identifying inefficient scripts.
- Remove anything that isn't required.
- Check for new scripts that are slowing down Page Speed regularly.
Having scripts on a website is a costly resource. They allow someone else to inject code into your site that we don't have control over, slowing down the rate at which people can view and engage with our content. This is done through HTML Code Injection/Cross-Site Scripting, and attackers often exploit HTML code injection vulnerabilities to gain access to user data within a web application. The hacker injects malicious HTML into a trusted website, executing untrusted scripts in the end user's browser. Because the browser cannot detect the malicious script, an attacker can gain access to session tokens, cookies, and other sensitive data that the browser stores. The ideal strategy to obtain good performance is to avoid using a script if possible.