The custom elements spec is not compatible with ES5 style classes. This
means ES2015 code compiled to ES5 will not work with a native
implementation of Custom Elements. To support browsers that natively
support Custom Elements but not ES2015 modules, we load
`@webcomponents/custom-elements/src/native-shim.js`, which minimally
augments the native implementation to be compatible with ES5 code.
(See [here][1] for more details.)
Previously, the shim was included in `polyfills.ts`, which meant it was
loaded in all browsers (even those supporting ES2015 modules and thus
not needing the shim).
This commit moves the shim from `polyfills.ts` to a `nomodule` script
tag in `index.html`. This will ensure that it is only loaded in browsers
that do not support ES2015 modules and thus do not needed the shim.
NOTE:
This commit also reduces size of the polyfills bundle by ~400B
(52609B --> 52215B).
[1]: https://www.npmjs.com/package/@webcomponents/custom-elements#es5-vs-es2015
PR Close#41162
d368fa2fa4