TypeScript example does not build

I was once able to build my es4x TypeScript application and pack it into a Docker image. However, my recent attempt to build the Docker images with latest documentation does not work. It seems that even the example TypeScript code does not build for me currently:

> empty-project@1.0.0 prestart /tmp/v/es4x/examples/typescript
> tsc

index.ts:1:23 - error TS2688: Cannot find type definition file for 'es4x'.

1 /// <reference types="es4x" />
                        ~~~~

Found 1 error.

npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! empty-project@1.0.0 prestart: `tsc`
npm ERR! Exit status 2
npm ERR! 
npm ERR! Failed at the empty-project@1.0.0 prestart script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /root/.npm/_logs/2021-04-19T09_10_53_837Z-debug.log

Version detail:

# node -v
v14.16.1
# npm -v
6.14.12
# java --version
openjdk 13.0.4 2020-07-14
OpenJDK Runtime Environment (build 13.0.4+8-Ubuntu-120.04)
OpenJDK 64-Bit Server VM (build 13.0.4+8-Ubuntu-120.04, mixed mode)

reactiverse / es4x

TypeScript example does not build #521