Load scripts asynchronously

load_script.js

const loadScript = (uri) => {
    return new Promise((resolve, reject) => {
        const el = document.createElement('script');
        el.type = 'text/javascript';
        el.src = uri;

        if (id) {
            const docEl = document.getElementById(id);
            if (docEl) {
                docEl.parentNode.removeChild(docEl);
            }
            el.id = id;
        }

        el.onload = () => {
            el.onload = el.onerror = null;
            if (resolve) {
                resolve();
            }
        };

        el.onerror = () => {
            el.onload = el.onerror = null;
            if (reject) {
                reject();
            }
        };

        document.head.appendChild(el);
    };
};

loadScript('http://path/to/script.js').then( 
    (data) => {
        console.log('success');
        console.log(data);
    },
    (error) => {
        console.log(error);
    }
);