You can check whether it exists and, if it does not exist, load it dynamically.
function loadScript(src) {
return new Promise(function (resolve, reject) {
var s;
s = document.createElement('script');
s.src = src;
s.onload = resolve;
s.onerror = reject;
document.head.appendChild(s);
});
}
async function load(){
if (!window.jQuery){
await loadScript(`https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js`);
}
console.log(jQuery);
}
load();