Svelte App on Older Browsers (IE11+)

index.html

<!-- generated via npm run build && npx create-polyfill-service-url analyse --file public/bundle.js -->

<script crossorigin="anonymous" src="https://cdn.polyfill.io/v3/polyfill.min.js?features=Array.from,Array.isArray,Array.prototype.entries,Array.prototype.fill,Array.prototype.filter,Array.prototype.forEach,Array.prototype.indexOf,Array.prototype.keys,Array.prototype.map,ArrayBuffer,console,DataView,Date.prototype.toISOString,document,fetch,Function.prototype.bind,globalThis,Map,Object.create,Object.defineProperties,Object.defineProperty,Object.entries,Object.getOwnPropertyDescriptor,Object.getOwnPropertyDescriptors,Object.getOwnPropertySymbols,Object.getPrototypeOf,Object.keys,Object.setPrototypeOf,Promise,Reflect,Reflect.construct,Set,Symbol,Symbol.iterator,WeakMap,WeakSet"></script>

rollup.config.js

import babel from 'rollup-plugin-babel'

...

production && babel({
    extensions: ['.js', '.mjs', '.html', '.svelte'],
    runtimeHelpers: true,
    exclude: [
      'node_modules/@babel/**'
    ],
    presets: [
      ['@babel/preset-env', {
        targets: '> 0.25%, not op_mini all'
      }]
    ],
    plugins: [
      '@babel/plugin-syntax-dynamic-import',
      ['@babel/plugin-transform-runtime', {
        useESModules: true
      }]
    ]
  })

terminal

npm i -D rollup-plugin-babel @babel/{preset-env,core} @babel/plugin-{syntax-dynamic-import,transform-runtime}