Title: async-javascript slows down website without doing anything
Last modified: September 16, 2021

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# async-javascript slows down website without doing anything

 *  [Tom](https://wordpress.org/support/users/godsdead/)
 * (@godsdead)
 * [4 years, 8 months ago](https://wordpress.org/support/topic/async-javascript-slows-down-website-without-doing-anything/)
 * Just installing this plugin makes my website come to a crawl, then when I run
   the Wizard it shows no speed improvements at all.
 * Could this be incompatible with my theme?
 * > [View post on imgur.com](https://imgur.com/1RZViCy)

Viewing 1 replies (of 1 total)

 *  Plugin Author [Optimizing Matters](https://wordpress.org/support/users/optimizingmatters/)
 * (@optimizingmatters)
 * [4 years, 8 months ago](https://wordpress.org/support/topic/async-javascript-slows-down-website-without-doing-anything/#post-14879095)
 * Hey Tom; typically asyncing or deferring JS will result in all parts of the page(
   UI) that are rendered by JS to be shown later, so in case of a JS-heavy site,
   the page might visually load slower, but then again JS-heavy sites are a usually
   a performance-buster anyway 😉
 * What is pretty weird in the wizard result overview, is the huge differences in
   total page size. As AsyncJS only adds async or defer flag to `<script` tags, 
   it does not impact page size. My best guess is that the deferring/ asyncing makes
   the JS load later (which is the goal), but in the meantime the “hero video” in
   the carousel keeps loading more data, thereby negatively impacting the performance
   as measured by GTmetrix.
 * What I would suggest; run a manual test on webpagetest.org (or pagespeed insights)
   without and with AsyncJS and compare some of the more relevant KPI’s (First Contentfull
   Paint, Largest Contentfull paint, onLoad time, cumulative layout shift, …).
 * hope this helps,
    frank

Viewing 1 replies (of 1 total)

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 * ![](https://ps.w.org/async-javascript/assets/icon-128x128.png?rev=1839260)
 * [Async JavaScript](https://wordpress.org/plugins/async-javascript/)
 * [Frequently Asked Questions](https://wordpress.org/plugins/async-javascript/#faq)
 * [Support Threads](https://wordpress.org/support/plugin/async-javascript/)
 * [Active Topics](https://wordpress.org/support/plugin/async-javascript/active/)
 * [Unresolved Topics](https://wordpress.org/support/plugin/async-javascript/unresolved/)
 * [Reviews](https://wordpress.org/support/plugin/async-javascript/reviews/)

 * 1 reply
 * 2 participants
 * Last reply from: [Optimizing Matters](https://wordpress.org/support/users/optimizingmatters/)
 * Last activity: [4 years, 8 months ago](https://wordpress.org/support/topic/async-javascript-slows-down-website-without-doing-anything/#post-14879095)
 * Status: not resolved