discourse-custom-wizard/assets/javascripts/wizard/lib/load-script.js.es6

import { ajax } from 'wizard/lib/ajax';
const _loaded = {};
const _loading = {};

function loadWithTag(path, cb) {
  const head = document.getElementsByTagName('head')[0];

  let finished = false;
  let s = document.createElement('script');
  s.src = path;
  if (Ember.Test) {
    Ember.Test.registerWaiter(() => finished);
  }
  head.appendChild(s);

  s.onload = s.onreadystatechange = function(_, abort) {
    finished = true;
    if (abort || !s.readyState || s.readyState === "loaded" || s.readyState === "complete") {
      s = s.onload = s.onreadystatechange = null;
      if (!abort) {
        Ember.run(null, cb);
      }
    }
  };
}

export function loadCSS(url) {
  return loadScript(url, { css: true });
}

export default function loadScript(url, opts) {

  // TODO: Remove this once plugins have been updated not to use it:
  if (url === "defer/html-sanitizer-bundle") { return Ember.RSVP.Promise.resolve(); }

  opts = opts || {};

  $('script').each((i, tag) => {
    const src = tag.getAttribute('src');

    if (src && (opts.scriptTag || src !== url)) {
      _loaded[tag.getAttribute('src')] = true;
    }
  });


  return new Ember.RSVP.Promise(function(resolve) {
    url = Discourse.getURL(url);

    // If we already loaded this url
    if (_loaded[url]) { return resolve(); }
    if (_loading[url]) { return _loading[url].then(resolve);}

    let done;
    _loading[url] = new Ember.RSVP.Promise(function(_done){
      done = _done;
    });

    _loading[url].then(function(){
      delete _loading[url];
    });

    const cb = function(data) {
      if (opts && opts.css) {
        $("head").append("<style>" + data + "</style>");
      }
      done();
      resolve();
      _loaded[url] = true;
    };

    let cdnUrl = url;

    // Scripts should always load from CDN
    // CSS is type text, to accept it from a CDN we would need to handle CORS
    if (!opts.css && Discourse.CDN && url[0] === "/" && url[1] !== "/") {
      cdnUrl = Discourse.CDN.replace(/\/$/,"") + url;
    }

    // Some javascript depends on the path of where it is loaded (ace editor)
    // to dynamically load more JS. In that case, add the `scriptTag: true`
    // option.
    if (opts.scriptTag) {
      if (Ember.testing) {
        throw `In test mode scripts cannot be loaded async ${cdnUrl}`;
      }
      loadWithTag(cdnUrl, cb);
    } else {
      ajax({url: cdnUrl, dataType: opts.css ? "text": "script", cache: true}).then(cb);
    }
  });
}