I’m trying to deploy my Node.js application to Heroku but keep running into this frustrating error. When I push my code using git push heroku master, everything seems to work fine at first. The build process starts normally and begins downloading dependencies like express, mongoose, and redis. However, it suddenly fails during the npm install phase with these error messages:
npm ERR! callback() never called!
npm ERR! not ok code undefined
npm ERR! callback() never called!
npm ERR! not ok code 1
! Failed to install --production dependencies with npm
! Heroku push rejected, failed to compile Node.js app
This prevents my deployment from completing and shows:
To [email protected]:my-app-name.git
! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to '[email protected]:my-app-name.git'
The weird thing is that this just started happening recently. My deployments were working perfectly fine last week. I haven’t changed my package.json or any major dependencies. Has anyone encountered this callback error before? What could be causing npm to fail during the Heroku build process?
omg i had that too! clearing the cache worked like a charm. just run heroku repo:purge_cache -a your-app-name and then try pushing again. it’s so frustrating when npm throws those errors outta nowhere, but this usually does the trick! good luck!
This callback error drove me nuts for days until I figured out it was corrupted dependencies in node_modules. Usually happens when npm’s cache gets messed up or packages don’t install completely, leaving callbacks hanging. Here’s what fixed it for me: delete your entire node_modules folder and package-lock.json, then run npm install fresh before pushing to Heroku again. Sometimes npm thinks dependencies are installed when they’re actually broken. Also check if you’ve got postinstall scripts in package.json that might be timing out or failing silently - those can cause callback errors too. Since this just started happening, it’s probably either npm registry issues or a recent dependency update that corrupted things.
Had this exact issue two months ago - it’s usually npm registry connectivity problems during build. The callback error happens when npm gets stuck waiting for the registry to respond. I fixed it by switching to a different npm registry. Just add an .npmrc file to your project root with registry=https://registry.npmjs.org/. Also check for private or scoped packages that might have auth issues. Heroku’s build environment sometimes has network hiccups that cause these callback failures. If switching registries doesn’t work, try locking your npm version in package.json with an engines field so your local environment matches Heroku’s build system.