I don't know if this website specifically did it, but a lot of other similar websites provide such services in a very bad way, for example base64encode.org and base64decode.org send your data to the server instead of using JS, and no one knows what they do with it.
I do understand that some still prefer browsers with JS disabled, but a website could probably detect this and default to in-browser processing, while reserving server-side to those edge cases.
I do understand that some still prefer browsers with JS disabled, but a website could probably detect this and default to in-browser processing, while reserving server-side to those edge cases.