js判断载入script

var script = document.createElement('script');
script.src = 'path/to/script.js';
script.onload = function() {
  console.log('Script has been loaded');
};
document.head.appendChild(script);

var script = document.createElement('script');
script.src = 'path/to/script.js';
script.onreadystatechange = function() {
  if (this.readyState == 'complete' || this.readyState == 'loaded') {
    console.log('Script has been loaded');
  }
};
document.head.appendChild(script);

function loadScript(url) {
  return new Promise((resolve, reject) => {
    var script = document.createElement('script');
    script.src = url;
    script.onload = resolve;
    script.onerror = reject;
    document.head.appendChild(script);
  });
}

loadScript('path/to/script.js')
  .then(() => console.log('Script has been loaded'))
  .catch(error => console.error('Failed to load script', error));