This causes serious breakage, but that's ok. Let's pick it up one small step at a time.
TEST RESULTS AFTER UPDATE
C:\ws\preact-helmet>npm test
> preact-helmet@5.0.0-alpha-1 pretest C:\ws\preact-helmet
> npm run clean && npm run lint && npm run compile
npm WARN invalid config loglevel="notice"
> preact-helmet@5.0.0-alpha-1 clean C:\ws\preact-helmet
> rimraf lib build es
npm WARN invalid config loglevel="notice"
> preact-helmet@5.0.0-alpha-1 lint C:\ws\preact-helmet
> eslint --ignore-path .gitignore -- .
C:\ws\preact-helmet\test\HelmetDeclarativeTest.js
5:19 error Unable to resolve path to module 'react' import/no-unresolved
6:22 error Unable to resolve path to module 'react-dom' import/no-unresolved
7:25 error Unable to resolve path to module 'react-dom/server' import/no-unresolved
8:9 error Helmet not found in '../src/Helmet' import/named
9:9 error HTML_TAG_MAP not found in '../src/HelmetConstants' import/named
10:35 error Unable to resolve path to module '../src/HelmetUtils.js' import/no-unresolved
C:\ws\preact-helmet\test\HelmetTest.js
4:19 error Unable to resolve path to module 'react' import/no-unresolved
5:22 error Unable to resolve path to module 'react-dom' import/no-unresolved
6:25 error Unable to resolve path to module 'react-dom/server' import/no-unresolved
7:9 error Helmet not found in '../src/Helmet' import/named
8:35 error Unable to resolve path to module '../src/HelmetUtils.js' import/no-unresolved
✖ 11 problems (11 errors, 0 warnings)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! preact-helmet@5.0.0-alpha-1 lint: `eslint --ignore-path .gitignore -- .`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the preact-helmet@5.0.0-alpha-1 lint 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! C:\Users\Frank\AppData\Roaming\npm-cache\_logs\2017-07-25T21_00_34_759Z-debug.log
npm ERR! Test failed. See above for more details.
This causes serious breakage, but that's ok. Let's pick it up one small step at a time.
TEST RESULTS AFTER UPDATE
SEE Update test suite based on v5 #23