To reduce the impact of third-party code in Wordpress, you can delay, run async or defer. The solution may depend on whether you consider the code essential and if it can run delayed/deferred.
One of the modern solutions is running your third-party code in a web worker to offload the main thread, but this approach isn’t fully compatible with Wordpress yet.
Use async or defer attribute
If it’s a marketing plugin that needs to have its metrics right and is critical, run it async, such as running a valuable Facebook ad campaign, in this case, run Facebook JS async.
Run with defer attribute when it needs to load after the initial load such as Google Analytics. Delay it when it’s used for collecting non-essential metrics.
Change iframes to JS or static
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