Load a script in the page programatically in javascript.

loadScript.js

function loadScript(src, { scriptId = '', insertBeforeAllTags = false } = {}) {
  return new Promise((resolve, reject) => {
    let script = document.createElement('script');
    script.id = scriptId;
    script.onload = resolve;
    script.onerror = event => {
      reject(new ExternalScriptError(event.target.src));
    };
    script.src = src;

    if (insertBeforeAllTags) {
      let firstScriptTagInDocument = document.getElementsByTagName('script')[0];
      firstScriptTagInDocument.parentNode.insertBefore(script, firstScriptTagInDocument);
    } else {
      document.body.appendChild(script);
    }
  });
}