title: Why am I getting "ReferenceError: 'TextEncoder' is undefined" in IE11 after importing the text-encoding polyfill?
body: <p>I am trying to pollyfill a library fetch-readablestream (<a href="https://github.com/jonnyreeves/fetch-readablestream" rel="noreferrer">https://github.com/jonnyreeves/fetch-readablestream</a>). I have added the polyfills and most things do work but I keep getting an error about TextEncoder <code>ERROR ReferenceError: 'TextEncoder' is undefined</code></p>
  
  <p>I've added the required pollyfills: web-streams-polyfill, text-encoding, and babel-polyfill. I tried other equivalents of these polyfills but I get the same issue.</p>
  
  <p>My <code>polyfills.ts</code> file after the required IE imports that I uncommented.</p>
  
  <pre><code>import 'web-streams-polyfill'; // Run `npm install --save web-streams-polyfill`.
  import 'text-encoding'; // Run `npm install --save text-encoding`.
  import 'babel-polyfill'; // Run `npm install --save babel-polyfill`.
  </code></pre>
  
  <p>I also tried adding scripts to <code>index.html</code></p>
  
  <pre><code>&lt;script src="node_modules/text-encoding/lib/encoding-indexes.js"&gt;&lt;/script&gt;
  &lt;script src="node_modules/text-encoding/lib/encoding.js"&gt;&lt;/script&gt;
  </code></pre>
  
  <p>I don't expect any errors but I get this:</p>
  
  <pre><code>ERROR ReferenceError: 'TextEncoder' is undefined
     "ERROR"
     {
        [functions]: ,
        __proto__: { },
        description: "'TextEncoder' is undefined",
        message: "'TextEncoder' is undefined",
        name: "ReferenceError",
        number: -2146823279,
        stack: "ReferenceError: 'TextEncoder' is undefined
     at responseParserFactory (http://localhost:4200/vendor.js:139703:3)
     at xhrTransport (http://localhost:4200/vendor.js:139960:1)
     at fetchStream (http://localhost:4200/vendor.js:139795:4)
     at DevicewiseService.prototype.getNotifications (http://localhost:4200/main.js:6577:9)
     at Anonymous function (http://localhost:4200/main.js:159:17)
     at SafeSubscriber.prototype.__tryOrUnsub (http://localhost:4200/vendor.js:145834:9)
     at SafeSubscriber.prototype.next (http://localhost:4200/vendor.js:145772:13)
     at Subscriber.prototype._next (http://localhost:4200/vendor.js:145715:5)
     at Subscriber.prototype.next (http://localhost:4200/vendor.js:145692:9)
     at MapSubscriber.prototype._next (http://localhost:4200/vendor.js:150984:5)",
        Symbol([[Cancel]])_g.r6fxkqwxet3: undefined,
        Symbol([[Pull]])_h.r6fxkqwxet3: undefined,
        Symbol(INITIAL_VALUE)_p.r6fxkqwxet3: undefined,
        Symbol(rxSubscriber)_o.r6fxkqwxet3: undefined
     }
  </code></pre>
  
  <p>We can see this happens in the fetchStream call.</p>