why i see this block time for script if I use script tag with defer

[pogran]

For site https://xn--80aaalhzvfe9b4a.xn--p1ai/ I see block time for script yandex.metrika with props defer how it possible?

[adamraine]

The defer attribute doesn't prevent the script from being run. It just defers it's execution until after the page is finished parsing:
https://www.w3schools.com/tags/att_script_defer.asp

Lighthouse still analyzes the page after the page is parsed, giving the script plenty of time to run and block the main thread.

[pogran]

@adamraine ok for my case what need to do with this? how to add metrics in code without block main thread?

[adamraine]

Ultimately, the script execution is what is blocking the main thread. Please see our existing docs on this topic:
https://developer.chrome.com/docs/lighthouse/performance/bootup-time/#how-to-speed-up-javascript-execution

[pogran]

@adamraine i see this point, but it not my script) i need to set setTimeout (i think it not a good chooise) for this if i want not to block main thread or mb i can use some events which tell me that main tread is free?

[adamraine]

Perhaps this will help: https://developer.mozilla.org/en-US/docs/Web/API/Window/requestIdleCallback

[pogran]

@adamraine no the same situation