load script

loadscript.js

<script>
function loadScript(url, callback) {
        let selector = 'script[src*="' + url + '"]';
        if (!document.querySelector(selector)) {
            let script = document.createElement("script");
            script.type = 'text/javascript';

            if (script.readyState) {  //IE
                script.onreadystatechange = function () {
                    if (script.readyState === 'loaded' ||
                        script.readyState === 'complete') {
                        script.onreadystatechange = null;
                        if (callback) {
                            callback();
                        }
                    }
                };
            } else {  //Others
                script.onload = function () {
                    if (callback) {
                        callback();
                    }
                };
            }

            script.src = url;
            document.body.appendChild(script);
        }
    }
    loadScript('js/vendor/jquery-3.5.1.min.js', () => {
        consol.log('loaded')
    });
</script>