I see, so you make edits, the Javascript edits the html, therefore File -> Save Page will download an html file with your changes in it that you can open again.
I forget that File -> Save is even a thing for websites.
I forget that File -> Save is even a thing for websites.
You have to click a save button in the app, and it will generate a valid copy. However, most users deploy some plugin or software which allows transparent auto-saving.
It's not perfect, though. Paragraphs are rendered by using two br tags, instead of p tags. Link syntax is the reverse of MediaWiki syntax; i.e. [[foo|bar]] links to "foo" in MediaWiki, but "bar" on TiddlyWiki, which trips me up constantly. There's other syntax awkwardness like sensitivity to spacing and newlines. Journals sort in alphabetical, not chronological order.