Dynamically load a script with callback (JS) or Promise (TS)

loadScript.js

function loadScript(id, src, async = true, onload = undefined, onerror = undefined) {
  var elScript = Object.assign(document.createElement('script'), {
    id, src, async, type: 'text/javascript'
  })
  if (onload) elScript.addEventListener("load", onload);
  if (onerror) elScript.addEventListener("error", onerror);
  document.head.appendChild(elScript)
}

loadScript.ts

export async function loadScript(id: string, src: string, async = true): Promise<void> {
  return new Promise((accept, reject) => {
    const elScript = Object.assign(document.createElement('script'), {
      id, src, async, type: 'text/javascript'
    })
    elScript.addEventListener("load", () => accept());
    elScript.addEventListener("error", () => reject('Failed to load ' + src));
    document.head.appendChild(elScript)
  })
}