Honestly, hoodoo throwing more code at it isn't the answer, but I guess when you're pretty much strictly CSR telling users with accessibility needs -- and therefor search engines -- to get stuffed, that's to be expected.

You want to make pageloads faster?

Move the SVG logo's and icons out of the markup so it can be cached and your server-side code doesn't have to waste time pasting them into the markup every time there's a page load. If you're worried about handshake counts since most of them are monochromatic, put them into a font.

Lose the Aria role nonsense that you wouldn't need if you had semantic markup; if that's too much to ask, maybe kill off all the empty ones bloating out the code or ones that have zero business in the markup - like the ones on the HTML tag?

Kill off 90%+ of the data- attributes for react that have no legitimate reason or purpose to exist in the markup other than to make the page slower. If react needs to hook your META tags, there's something horrifyingly wrong with how you're building the site. Though that's just react and why I rail against its use.

Lose the redundant opengraph values that serve zero legitimate purpose when they'll fall-back on your non-og equivalent. (99% of the time there's no real reason to use anything more than og:image)

Stop wasting bandwidth on presentational classes. Say what things are not what you want them to look like. If you're using classes like "left-items flex-grow-1 d-flex flex-row align-items-center" you're doing it all wrong. As I often say if you want HTML to work that way, you must really miss HTML 3.2.

If you have HTML elements that only serve a purpose for client side scripting, they have no business in your HTML in the first place. Generate all of them from the scripting -- where they can be cached instead of on each and every pageload.

There's a reason where you have this 7k of minified code:

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Anyone who actually knows how to use HTML would use this:

<div id="top">
    <h1><a href="/">Hashnode</a></h1>
    <ul id="mainMenu">
        <li><a href="/">Home</a></li>
        <li>
            <input type="checkbox" id="mainMenu_postsToggle">
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Assuming one is ok with abusing a checkbox with :checked for the submenu show/hide. Be even less markup if you wanted to rely on a JS only solution.

That's 1/15th the code that would have to be sent on subsequent pageloads. There's a reason when I say people using things like react, bootstrap, and other such crutches are making themselves work harder, not smarter -- because you're making massive convoluted non-semantic inaccessible messes of it with anywhere from two to twenty times the code needed to do the job! That's why it's slow.

As evidenced by the home page of this site right this moment for a non-logged in guest, takes 3 megabytes in 33 separate files just for the HTML, CSS, JavaScript, and XHR present, all to deliver 2.03k of plaintext, maybe two dozen links, and not even a half dozen content media elements -- not even 10k of HTML's job. Much less given the relative simplicity of this site's design it being highly unlikely for the entire site to need more than 48k of CSS in one or two files. Add on the endless horde of JavaScript with no scripting off graceful degradation...

Literally, 90k of HTML doing 10k's job. Nearly a megabyte of CSS in six files doing 48k or less in one or two files' job. Almost two megabytes of JavaScript in two dozen files doing stuff that the lions share of which shouldn't even be having scripting thrown at it!

In handshakes alone the realtime overhead for the majority of the world who doesn't have "magic perfect ultra-fiber broadband" comes to anywhere from 5 to 25 seconds just for the code. That's first-load, but the checks and/or sheer volume of it blowing out many browsers cache limits (the reason all that playing with cache-control headers placebo BS doesn't actually work for people who visit more than two websites a day no matter what Google says) still means "hey has this been updated" requests are gonna hurt.

So not only would such optimization of the code by kicking bootstrap to the curb and reigning in (if not just killing off) react result in faster subsequent visits, it would also speed up initial pageloads.

Of course, you're knee deep in it, so simply getting a stick to -- as I often joke -- "scrape off the bootcrap" is gonna hurt, since we're basically talking a complete rewrite to deal with bad choices in frameworks. But then you know me, IMHO there is no such thing as a good front-end framework for web development. They make you write two to five times the code needed, deploy five to twenty times the code needed, spread stuff out over dozens of separate files when there's no reason to have more than 3 to 5 of them (not counting social plugins, but even those can be bamboozled into behaving).

Throwing some fancy "service" and more code at it isn't the answer. Thanks to the choices of technologies you've got a 5+ megabyte homepage spanning 80+ files before lazy-loading even kicks in -- where more than half of that could be pitched in the can -- and you're worried about screwing around with wasting bandwidth on precaching after the fact, playing games figuring out what the user's connection speed is, and figuring out what links are in the viewport?

Sorry, but like a lot of things Google is doing lately, waste of time, waste of bandwidth, waste of code to correct for poor architectural choices.

Again, exactly the type of failings I go into banks, healthcare, public utilities, and government agencies to send to the nether realms like the reaper leading the horsemen of the apocalypse.