JavaScriptやCSSを遅延ロードする方法

<script>
//<![CDATA[ 
function lazyLoadScript(scriptSrc) {

    var scrollFirstTime = 1;

    //スクロールorマウスクリックor画面タッチで発火
    window.addEventListener("scroll", oneTimeFunction, false);
    //window.addEventListener("mousedown", oneTimeFunction, false);
    //window.addEventListener("touchstart", oneTimeFunction, false);
    //window.addEventListener("mousemove", oneTimeFunction, false);

    function oneTimeFunction() {
        if (scrollFirstTime === 1) {

            scrollFirstTime = 0;
            var adScript = document.createElement("script");
            adScript.src = scriptSrc;

            document.body.appendChild(adScript);
            window.removeEventListener("scroll", oneTimeFunction, false);
            //window.removeEventListener("mousedown", oneTimeFunction, false);
            //window.removeEventListener("touchstart", oneTimeFunction, false);
            //window.removeEventListener("mousemove", oneTimeFunction, false);

        }
    }
}

//遅延読み込みするjavascript
lazyLoadScript("https://platform-api.sharethis.com/js/sharethis.js#property=xxxx&product=inline-reaction-buttons");
lazyLoadScript("https://xxxx/prism121.js");
lazyLoadScript("https://platform.twitter.com/widgets.js");
//]]>
</script>

/*Your Script is here to maintain performance.*/

//Defer.jsで遅延読込みさせる外部参照ファイル
var deferUrl1 = 'https://platform.twitter.com/widgets.js';
var deferUrl2 = 'https://platform-api.sharethis.com/js/sharethis.js#property=5f4aad10ec6f5100126117d9&product=inline-reaction-buttons';
var deferUrl3 = 'https://code.heavy-peat.com/prism121.js';
var deferUrl4 = 'https://code.heavy-peat.com/prismJS118.css';
var deferUrl5 = 'https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.15.3/css/all.min.css';
var deferUrl6 = 'https://cpwebassets.codepen.io/assets/embed/ei.js';
var deferUrl7 = 'https://fundingchoicesmessages.google.com/i/pub-5860764237864409?ers=1';
var deferUrl8 = 'https://assets.bluesky.lol/js/b1.js';

//遅延表示させるクラス
const selector1 = 'lazy-twitter-tweet'; // 遅延読み込みさせるダミーのクラス
const selector2 = 'lazy-twitter-timeline'; // 遅延読み込みさせるダミーのクラス
const selector3 = 'sharethis-inline-reaction-buttons';
const selector4 = 'twitter-tweet';
const selector5 = 'twitter-timeline';
const selector6 = 'lbluesky-widget';

const embed1 = document.getElementsByClassName(selector1);
const embed2 = document.getElementsByClassName(selector2);
const embed3 = document.getElementsByClassName(selector3);
const embed4 = document.querySelectorAll('[class*="language-"]');
const embed5 = document.getElementsByClassName('fas');
const embed6 = document.getElementsByClassName('codepen');
const embed7 = document.getElementsByClassName(selector6);

try {
    //TwitterのJavaScriptとDomの遅延読込み
    if (embed1.length !== 0 || embed2.length !== 0) {
        Defer.js(deferUrl1, 'widgets-js', 1000, function() {
            Defer.dom('.lazy-twitter-tweet, .lazy-twitter-timeline', 200, null, function(node) {
                if (node.className === 'lazy-twitter-tweet') {
                    node.className = 'twitter-tweet tw-align-center'; // 遅延読み込みさせるオリジナルのクラスに置き換える
                } else {
                    node.className = 'twitter-timeline'; // 遅延読み込みさせるオリジナルのクラスに置き換える
                }
                twttr.widgets.load(node.parentNode);
            }, { rootMargin: "200%" });
        });
    }
    //sharethisのJavaScriptの遅延読込み
    if (embed3.length !== 0) {
        Defer.js(deferUrl2, 'sharethis-js', 1000);
    }
    //prismのJavaScriptとcssの遅延読込み
    if (embed4.length !== 0) {
        Defer.js(deferUrl3, 'prism-js', 1000, function() {
            Defer.dom('pre code', 200, 'scroll-loaded-prism', Prism.highlightElement, { rootMargin: "120%" });
        }, true);
        Defer.css(deferUrl4, 'prism-css', 1000);
    }
    //font-awesomeのcssを遅延読込み
    if (embed5.length !== 0) {
        Defer.css(deferUrl5, 'font-awesome-css', 1000);
    }
    //CodepenのJavaScriptの遅延読込み
    if (embed6.length !== 0) {
        Defer.js(deferUrl6, 'codepen-js', 1000);
    }
    //広告ブロックによる損失収益の回復タグのJavaScript遅延読込み
    Defer.js(deferUrl7, 'ad-blocker-js', 1000);
    //BlueSkyのJavaScriptとDomの遅延読込み
    if (embed7.length !== 0) {
        function createWidget(node) {
            var id = node.getAttribute('id');
            Defer.js(deferUrl8, {
                'data-handle': id.replace(/-[^-]+$/, ''),
                'data-skeet': id.replace(/^.*-/, '')
            });
        }
        Defer.dom('.bluesky-widget', 0, 'shown', createWidget, {
            rootMargin: "120%"
        });
    }
} catch (error) { console.log(error) }