IE 11 compatibility

[pavelekNET]

Describe the bug
In IE 11 file morphism.js throws "Invalid syntax (1,1715)"

To Reproduce
Steps to reproduce the behavior:

1. reference <script src="https://unpkg.com/morphism/dist/morphism.js"></script>
2. Open in IE 11

Expected behavior
Work like in other browsers

Additional context
If possible could you specify at least polyfills that are required for this library? I found out that its used: Promise, Map

Many thanks

[priithansen]

There are also arrow functions in dist build that IE doesn't support

[emyann]

Thank you guys for digging this issue! I'm gonna work on a PR by the end of the week, when I'll be able to test on IE11.

[priithansen]

I was able to produce a IE compatible build with:

npm i --save-dev @babel/plugin-transform-runtime
npm i --save-dev @babel/runtime

and modifing the .babelrc file so:

{
  "presets": [
    [
      "@babel/preset-env",
      {
        "targets": {
          "node": "current",
          "esmodules": true,
          "ie": "11", // Added !
        }
      }
    ],
    "@babel/typescript"
  ],
  "plugins": [
    ["@babel/plugin-proposal-decorators", { "legacy": true }],
    ["@babel/proposal-class-properties", { "loose": true }],
    "@babel/proposal-object-rest-spread",
    "@babel/plugin-transform-runtime" // Added !
  ]
}

But this result still needs unspecified polyfills (ex: Symbol) and will not work if transpiled again on import by the consumer script. Also the file size will end up ~2x the original size.

Can't speak for other people but for my use case it would make most sense if the npm install of morphism would include js source so that I could import and tell webpack to transpile it and use whichever polyfills or targets are specified for the whole project.

[sisp]

@emyann Have you considered using TSDX for zero-config build/test setup? It follows the spirit of Facebook's Create React App but for (Typescript) libraries instead of React apps. Many great projects like Formik, mobx-keystone, mobx-react-lite, etc. are using it and my personal experience has been great, too. It takes care of many peculiarities out of the box and is easily extensible if needed. Perhaps it also helps with IE11 compatibility?