SharePoint Custom Scripts
Microsoft is proceeding with the staged retirement of custom scripts across SharePoint Online and OneDrive. Here is what an admin needs to know.
Quick Introduction to SharePoint “custom scripts”
In SharePoint, “custom scripts” broadly refers to client‑side code (Javascript) added to pages. Custom scripts were actively used for sites customizations, and still present in “classic” features (like “script editor web part”). Today Microsoft consider custom scripting in SharePoint Online as a Security risk. Custom scripts can execute with the current user’s permissions, making it hard to govern what code runs, who added it, and where it loads resources from—opening doors to script injection, XSS, and compliance/performance issues. See more here.