When NPM miss with Heroku, How To Solve (npm ERR! Failed at the <module> start script).

Important

• This Article supposes you working with the nuxt-express starter template. But I think it's a global issue that might happen with React and Next or may happen in general.
• You can go to the solution section and you will be good to go. The rest is just if you are interested enough.

Boring talk

It's a weird problem that turned my life into hell for long long time. NPM doesn't install the dependencies. For some reason I like Heroku, simple and just work. But when I started to use Nuxt with express and deploy the app to Heroku I started to get this issue. Every time I spend the whole day tying to figure out what did I do to make this happen but I did nothing. A normal deployment. And then I create a new project, copy all the logic from the old project to the new one and install the same packages. and sometimes it doesn't work as well so I create a new app in Heroku and do the same thing again and again till it work. Sometimes I go with another solutions -like Vercel or Portal Azure- but it doesn't feel like home if you know what i mean. But today I figured out a way to solve this issue finally.

Why this happens?

I don't know exactly why this happens lol. But after I read Heroku Node.js support I found out that Heroku doesn't run npm i to install the dependencies instead it runs npm ci.

If you want to know the difference about the two you can find it here. But In short, the main differences between using npm install and npm ci are:

• The project must have an existing package-lock.json or npm-shrinkwrap.json.
• If dependencies in the package lock do not match those in package.json, npm ci will exit with an error, instead of updating the package lock.
• npm ci can only install entire projects at a time: individual dependencies cannot be added with this command.
• If a node_modules is already present, it will be automatically removed before npm ci begins its install.
• It will never write to package.json or any of the package-locks: installs are essentially frozen.

So I configured Heroku to use npm i and also disabled cache to make sure every time I deploy the app it reinstall everything.

The solution

First of all I specified my Node and NPM versions in my package.json you can know the exact versions with those commands:

for Node:

node -v

and for NPM:

npm -v

then in add both of them in your package.json like this:

"engines": {
  "npm": <Your npm version>,
  "node": <Your node version>
}

As I said before you need to configure Heroku to use npm i instead of npm ci and to disable Heroku Cache. you can do this in two ways.

• The first one you can use the Heroku CLI :

  1- Make sure you're logged in with your Heroku account
  

  heroku login
  

  2- Use these commands to do the trick
  

  $ heroku config:set USE_NPM_INSTALL=true -a <Your app name>
  $ heroku config:set NODE_MODULES_CACHE=false -a <Your app name>
  

• The second way is to do it from Heroku itself

  1- Go to your app in Heroku and in the Settings tab

  

  2- scroll to 'reveal config vars' button

then add

index	key	value
1	NODE_MODULES_CACHE	false
2	USE_NPM_INSTALL	true

you should end up with something like this

Don't forget to add your other env variables :)
I wish this ends the suffer.

Comments

[TT7 Aden]

Thank you very much you save my time.

[Aymoon]

Glad to hear that 💙