Many use cases are too complex to summarize in a short demo. The listed open source projects use SheetJS libraries in clever deployments.
Deployment: Visual Studio Code Extension
Website: https://marketplace.visualstudio.com/items?itemName=RandomFractalsInc.vscode-data-preview
Repository: https://github.com/RandomFractals/vscode-data-preview
Notes: Demonstrates reading and writing files.