Xumm xApp Javascript SDK 
Part of the "Xumm Universal SDK", which is the preferred way of interacting with the Xumm ecosystem from JS/TS environments: https://www.npmjs.com/package/xumm - https://github.com/XRPL-Labs/Xumm-Universal-SDK
Easily interact with Xumm from your xApp (frontend).
Documentation: see: https://xumm.readme.io/docs/xapp-xumm-ui-interaction
NPM: https://www.npmjs.com/package/xumm-xapp-sdk
CDN (browser):
A browserified version (latest) is available at JSDelivr & direclty from the xumm.app domain:
<script src="https://xumm.app/assets/cdn/xumm-xapp-sdk.min.js"></script>