### Code to prevent this error:
```
polymer-fn.js:43 Uncaught (in promise) DOMException: Failed to execute 'define' on 'CustomElementRegistry': this name has already been used with this registry
at Polymer
```
#### You just have to add before this line:
```
window.customElements.define('my-app', MyApp);
```
#### This is the code that will solve the problem:
```
const _customElementsDefine = window.customElements.define;
window.customElements.define = function(name, clazz, config) {
if (!customElements.get(name)) {
_customElementsDefine.call(window.customElements, name, clazz, config);
}
};
```
#### This is necessary to import the paper-dropdown-menu
```
import '@polymer/paper-item/paper-item.js';
import '@polymer/paper-listbox/paper-listbox.js';
import '@polymer/paper-dropdown-menu/paper-dropdown-menu.js';
```
#### And you need this package
```
npm install web-animations-js --save
```
#### And make sure to add the animations this way:
```
<script src="node_modules/web-animations-js/web-animations-next-lite.min.js"></script>
```
Before loading your application
Gitlab runner in .gitlab-ci.yml
```
she-profiles-backend:
script:
- docker run -v test:/etc/newman -t postman/newman_ubuntu1404 run "https://www.getpostman.com/collections/e893b0ef2d69964f9661"
- polymer build
```