Load global javascript

load_script.js

function loadScript(url, onload) {
    fetch(url)
    .then(function(response) {
        if (!response.ok) {
            throw new Error(`HTTP error. Status: ${response.status}`);
        }
        return response.blob();
    })
    .then(function(blob) {
        let objectUrl = URL.createObjectURL(blob),
        el = document.createElement("script");
        el.src = objectUrl;
        el.setAttribute("type", "text/javascript");
        el.async = true;
        el.onload = function(ev) {
            return onload(ev);
        };
        el.onerror = function(ev) {
            throw new Error(`Error running ${url}`);
        };
        document.body.appendChild(el);
    });
}

/*
loadScript(`/test.js`, function(ev) {
    console.log(test_var);
});
*/