How to defer parsing of JavaScript in Magento 2

Defer JavaScript means that JavaScript files loading will be delayed until parsing the page content finishes. Therefore, a browser loads all content before JavaScript files, which makes Magento sites perform faster than loading everything at the same time.

Beside deferring JavaScript manually by changing codes, admin can install an extension also called Defer JavaScript for Magento 2 to improve site speed and enhance customer experience effectively.

• Automatically defer parsing of JavaScript by delaying JavaScript loading till the last moment after all HTML and CSS files
• Improve page speed score when testing with GTMetrix

+ After installing Defer JavaScript:

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+ Before installing Defer JavaScript:

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Check it out for FREE Installation - FREE 1-year Support and FREE Updates!

For Magento 1 website, there is also Defer JavaScript extension to install with the same functions:
- Defer JavaScript loading until HTML and CSS loading is finished
- Defer Iframes loading effectively
- Improve site ranking on search engine