Everything that's in the src directory will get copied to deploy/public on build, which means that this file will get served at https://design-system.service.gov.uk/tsconfig.json.

Not a major issue but doesn't seem ideal either – any way we could move these into the base config but only apply them to src?

Thanks for taking a look at this

Good point! I've filtered it out using Metalsmith's .ignore()

We could move it to the base but we need to scope only ./src to "lib": ["ESNext", "DOM"]

Will likely want the compiler to check ./lib and ./tasks in future, but without DOM libraries

As this isn't really 'our' script, would it make more sense to turn off all type checking for the snippet?

I'm happy with that. Added // @ts-nocheck like we did for polyfills in the past

I guess we might follow up and change this to throw errors, but at the minute this has potential to trip us up by silently swallowing errors.

Given that $successNotification is only used within showSuccessNotification, could we move the lookup there, and return early if the banner isn't present?

That way at least the rest of the cookie page functionality will continue to work if the banner is missing for some reason.

Good thinking

I've copied what we do elsewhere for optional selectors

const $successNotification = $module.querySelector('.js-cookies-page-success')
if ($successNotification instanceof HTMLElement) {
  this.$successNotification = $successNotification
}

☝️ Avoid appending to class property unless checks pass, but check again in showSuccessNotification()