Read the blog post or see the source code.
Both cases are arrays of numbers 0-255. The first stores those arrays in Indexed DB directly, and the second encodes them to base64 and stores them as a string.
To measure your own device, choose "My device" from the drop-down at the top of the page and click "Record my stats".
If you have results for a different platform, please paste the code below into a new issue at codeberg.org/andybalaam/indexed-db-perf/issues. Explain what browser, operating system and architecture (e.g. Intel, M1, Raspberry Pi) you are using. Thanks!