Locally my code (custom element) works I can run “npm run serve” and use the element in developer mode in WeWeb. Also “npm run build” works without errors.
Where can I see the log of the build when uploading the component into “Coded components”. It just says Building and then in the end says CODEBUILD_FAILED but there is no error message! No log file or anything. This is a stopper for us, where can I please find the log file?
You need to request this from WeWeb - very unpractical, but it’s how it is. Talk to them in the in-app chat. Usually the build fails when you have some issues like syntax errors, wrong imports etc. We’ve had our fair share of fights with the components, but all ended successfully 
it may be a difference in the environment where the build is executed. maybe you have some global package installed locally. have you tried to build on a clean instance of node? (things like nvm or volta can help you)
here in the community we may be ble to help you with a list of dependencies.