Paper Drop Down Error

Running 14.0.13 is fine, tried to go to 14.1.20 and when our software starts up, all is fine at the Login Screen, but when we go to the next screen (menu, etc.) this error is caught by Chrome and our screen looks like the styles are not applied.

Uncaught Error: A custom element with name ‘dom-module’ has already been defined.
at Zd (webcomponents-sd-ce.js:145)
at Q.n.define (webcomponents-sd-ce.js:145)
at Q.Rf.define (webcomponents-sd-ce.js:197)
at eval (webpack-internal:///…/node_modules/@polymer/paper-dropdown-menu/node_modules/@polymer/polymer/lib/elements/dom-module.js?babel-target=es6:181)
at Module…/node_modules/@polymer/paper-dropdown-menu/node_modules/@polymer/polymer/lib/elements/dom-module.js?babel-target=es6 (VAADIN/build/vaadin-bundle-fef654298c2d6431b2e1.cache.js:625)
at webpack_require (VAADIN/build/vaadin-bundle-fef654298c2d6431b2e1.cache.js:20)
at eval (webpack-internal:///…/node_modules/@polymer/paper-dropdown-menu/node_modules/@polymer/polymer/lib/utils/style-gather.js?babel-target=es6:10)
at Module…/node_modules/@polymer/paper-dropdown-menu/node_modules/@polymer/polymer/lib/utils/style-gather.js?babel-target=es6 (VAADIN/build/vaadin-bundle-fef654298c2d6431b2e1.cache.js:1021)
at webpack_require (VAADIN/build/vaadin-bundle-fef654298c2d6431b2e1.cache.js:20)
at eval (webpack-internal:///…/node_modules/@polymer/paper-dropdown-menu/node_modules/@polymer/polymer/lib/mixins/element-mixin.js?babel-target=es6:8)

Hi Bob. We’ve had some issues with npm when updating versions - can you please try by removing

  • target folder
  • node_modules folder
  • package-lock.json
  • package.json
    and building the project again. It will take a while as everything is recreated but any possible conflicts bringing in multiple frontend dependencies should be fixed. In case the error still reproduces, then please file an issue to and please include the versions used (14.0.13 & 14.1.20) and the resulting package.json & target/frontend/package.json file.

We get these reports way too often when updating between 14.0 and 14.1 and have not been able to yet determine the cause. For 14.2 (currently in alpha) we’ve switched to use pnpm instead of npm as it handles the updates better.

Thank you. It did not work. I’ll post an issue as you recommend. Glad you’re moving to some other way of updating files.

I thought this was resolved…but it happens randomly. I now have to think if I can develop like this or go back to 14.0.13. I did delete the cahce of NPM and that helped, but now I get it randomly.