Heroku nodejs build failing: "Invalid semver requirement" - heroku

Question

I'm having a heap of trouble deploying my nodejs app to heroku. While it works perfectly for an initial build (to an empty application in heroku) any subsequent updates that I push fail.
I have defined the node version as "8.9.x", but if I define the exact version number of the latest version, it still fails - saying that "8.9.4" is not a valid semantic version.
If I take the engines section out of my package.json entirely, it tries to resolve "8.x" and then says that "8.x" isn't a valid semantic version!
Is there anything else that I could stuff up in my package.json to cause this? Or can anything outside the package.json be causing this?
Here's the output when pushing to the heroku git repo:
remote: Compressing source files... done.
remote: Building source:
remote:
remote: -----> Deleting 2 files matching .slugignore patterns.
remote: -----> Node.js app detected
remote:
remote: -----> Creating runtime environment
remote:
remote: NPM_CONFIG_LOGLEVEL=error
remote: NPM_CONFIG_PRODUCTION=true
remote: NODE_VERBOSE=false
remote: NODE_ENV=production
remote: NODE_MODULES_CACHE=true
remote:
remote: -----> Installing binaries
remote: engines.node (package.json): 8.9.x
remote: engines.npm (package.json): 5.6.x
remote:
remote: Resolving node version 8.9.x...
remote: Error: Invalid semantic version "8.9.x"
remote:
remote: -----> Build failed
remote:
remote: ! Invalid semver requirement
remote:
remote: Node, Yarn, and npm adhere to semver, the semantic versioning convention
remote: popularized by GitHub.
remote:
remote: http://semver.org/
remote:
remote: However you have specified a version requirement that is not a valid
remote: semantic version.
remote:
remote: https://kb.heroku.com/why-is-my-node-js-build-failing-because-of-an-invalid-semver-requirement
remote:
remote: ! Push rejected, failed to compile Node.js app.
remote:
remote: ! Push failed
remote: Verifying deploy...
remote:
remote: ! Push rejected to [app name].
remote:
And here is my package.json
{
"name": "[REDACTED]",
"version": "3.4.4",
"description": "[REDACTED]",
"main": "index.js",
"engines": {
"node": "8.9.x",
"npm": "5.6.x"
},
"scripts": {
"test": "index.js",
"start": "node index.js"
},
"repository": {
"type": "git",
"url": "git+https://[REDACTED]"
},
"author": "jasonalex",
"license": "SEE LICENSE IN LICENSE",
"bugs": {
"url": "https://[REDACTED]"
},
"homepage": "https://[REDACTED]",
"dependencies": {
"#google-cloud/logging-winston": "^0.7.0",
"#google-cloud/storage": "^1.5.2",
"#google-cloud/trace-agent": "^2.4.1",
"body-parser": "^1.18.2",
"cors": "^2.8.4",
"cron": "^1.3.0",
"express": "^4.16.2",
"filereader": "^0.10.3",
"firebase-admin": "^5.8.1",
"jsonwebtoken": "^8.1.1",
"lodash": "^4.17.4",
"mailgun-js": "^0.14.2",
"moment": "^2.20.1",
"multer": "^1.3.0",
"pdfkit": "^0.8.3",
"pdfmake": "github:bpampuch/pdfmake",
"twilio": "^3.11.1",
"websocket-driver": ">=0.5.1",
"winston": "^2.4.0",
"xmlhttprequest": "^1.8.0"
},
"devDependencies": {
"babel-eslint": "^7.2.3",
"eslint": "^4.16.0",
"eslint-plugin-react": "^7.5.1",
"localtunnel": "^1.8.3"
}
}

Answer 1

Okay well I feel a bit silly now - in my case i had added a config var in my heroku settings called 'platform' which was interfering with the official nodejs buildpack.
Removing/renaming this variable has cleared the problem right up.