I’ll build this as a single HTML document with embedded CSS/JS. Since the article’s real font file is external, the demos will use generated binary payloads so the OPFS behavior is testable without network or third-party assets. OPFS Large File Reads and Writes Demo

Stop Using IndexedDB; Use OPFS for Large File Reads and Writes

Interactive notes based on the article by zhangxinxu, published September 3, 2026. Original source: https://www.zhangxinxu.com/wordpress/?p=12379

1. Estimate Browser Storage and OPFS Support

Code:
Result:
Click the button to query this origin's storage estimate.
OPFSNot checked
QuotaNot checked
UsageNot checked
PersistedNot checked

2. Create, Write, and Read a Private File

Code:
Result:
Write a note into OPFS, then read it back from the private file system.

3. Cache a Large Binary Payload Like a Font File

Code:
Result:
The first run creates a generated 3 MB binary file. Later runs read it from OPFS.

4. Append Writes Without Rebuilding the Whole File

Code:
Result:
Append several lines to see byte-position writes in action.

5. OPFS Fits Files, IndexedDB Fits Indexed Records

Code:
Result:
Click to render a compact decision table.