title: Function.prototype.toString issues in IE11 Svelte/Babel/Rollup
body: <p>My current rollup.config.js is</p>
  
  <pre class="lang-js prettyprint-override"><code>    commonjs(),
      babel({
                  extensions: ['.js', '.mjs', '.html', '.svelte'],
                  runtimeHelpers: true,
                  exclude: ['node_modules/@babel/**', 'node_modules/core-js/**' ], // &lt;= /!\ NOT 'node_mobules/**'
                  presets: [
                      ['@babel/preset-env', {
                      // adapter to ensure IE 11 support
                      targets: '&gt; 0.25%, not dead, IE 11',
                      "modules": false,
                      "spec": true,
                      "forceAllTransforms": true,
                      useBuiltIns: 'usage',
                      corejs: 3
                      }]
                  ],
                  plugins: [
                      '@babel/plugin-syntax-dynamic-import',
                      [
                          '@babel/plugin-transform-runtime',
                          {
                              useESModules: true
                          }
                      ]
                  ]
                })
  </code></pre>
  
  <p>Getting issue in IE11:</p>
  
  <blockquote>
    <p>Function.prototype.toString: "this" is not a Function object</p>
  </blockquote>
  
  <p>How to correctly fix that issue?</p>
  
  <p>I have tried to </p>
  
  <ul>
  <li><p>import <a href="https://github.com/webcomponents/polyfills/tree/master/packages/webcomponentsjs" rel="nofollow noreferrer">webcomponents</a> into my main.js:</p>
  
  <p>import 'node_modules/@webcomponents/webcomponentsjs/webcomponents-bundle.js';</p>
  
  <p>But this file is not being imported: </p>
  
  <blockquote>
    <p>Unresolved dependencies <a href="https://rollupjs.org/guide/en/#warning-treating-module-as-external-dependency" rel="nofollow noreferrer">https://rollupjs.org/guide/en/#warning-treating-module-as-external-dependency</a>
    node_modules/@webcomponents/webcomponentsjs/webcomponents-bundle.js
    (imported by src\main.js)</p>
  </blockquote></li>
  </ul>
  
  <p>This means i have to config
     <a href="https://github.com/rollup/rollup-plugin-node-resolve" rel="nofollow noreferrer">resolve-plugin</a> but it seems to be incorrect way because it is marked as non-used then.</p>