exploring ie11 support

[chase-moskal]

1. i'm trying to see if i can get es-module-shims working in ie11

2. i created an es5 branch of es-module-shims, which uses babel to generate an es5 script es-module-shims.es5.js

3. in my repo for a web component i'm working on, i've included polyfills and am using es-module-shims.es5.js as follows

   <script src="https://unpkg.com/@babel/[email protected]/dist/polyfill.min.js"></script>
   <script src="https://unpkg.com/[email protected]/dist/fetch.umd.js"></script>
   <script>
     // inject console logging for each 'fetch' call
     var f = window.fetch
     window.fetch = function() {
       console.log("fetch", arguments[0])
       return f.apply(window, arguments)
     }
   </script>
   <script src="https://unpkg.com/@webcomponents/[email protected]/webcomponents-bundle.js"></script>
   <script type="importmap-shim" src="dist/importmap.json"></script>
   <script type="module-shim" src="source/demo.js"></script>
   <script src="assets/es-module-shims.es5.js"></script>

4. other browsers are working, but when source/demo.js goes to import "./register-all.js", ie11 incorrectly issues a request for /register-all.js instead of resolving it to source/register-all.js — in other words, in ie11, a request is made for register-all.js at the server root, not within source/

   // CHROME 71
   fetch http://localhost:5000/dist/importmap.json
   fetch http://localhost:5000/source/demo.js
   fetch http://localhost:5000/source/register-all.js
    // continues to load application
   
   // INTERNET EXPLORER 11
   fetch http://192.168.1.73:5000/dist/importmap.json
   fetch http://192.168.1.73:5000/source/demo.js
   fetch http://192.168.1.73:5000/register-all.js
    // fetch for "/register-all.js" fails with 404
   

let me know if you have a hunch about what might be going on, or if perhaps there could be further reasons of which i'm not yet aware that could make ie11 support impossible

[guybedford]

Yes this project doesn't support IE11, rather the recommendation for these environments is to compile ES modules into the System.register format and use SystemJS, which also supports import maps - https://github.com/systemjs/systemjs, as that ensures exact semantics equivalence.

But in many cases you might not even need import maps and exact semantics equivalence such that any other legacy workflow could apply (shimport / single-file builds / etc).