inject-js.js

function injectScript(src) {
    return new Promise((resolve, reject) => {
        const script = document.createElement('script');
        script.async = true;
        script.src = src;
        script.addEventListener('load', resolve);
        script.addEventListener('error', () => reject('Error loading script.'));
        script.addEventListener('abort', () => reject('Script loading aborted.'));
        document.head.appendChild(script);
    });
}

injectScript('http://example.com/script.js')
.then(() => {
    console.log('Script loaded!');
}).catch(error => {
    console.log(error);
});