The web-cache command manages the precompiled Fern library cache used for web builds, significantly reducing build times.
Usage Actions Show cache status and information
Remove the web build cache
Force rebuild of the cache
How It Works When building for web, Fern uses Emscripten to compile C++ to WebAssembly. To speed this up:
First web build : Fern compiles the entire framework (~30 seconds) and caches the resultSubsequent builds : Only your code is compiled (~5 seconds), linking against the cached libraryAuto-rebuild : Cache is automatically rebuilt if Fern source files change
The cache is stored in ~/.fern/cache/web/libfern_web.a.
Examples Check Cache Status Fern Web Cache Status ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Web cache is available Cache location: ~/.fern/cache/web Library file: libfern_web.a Size: 2.4 MB Last modified: 2024-03-15 14:32:18 Source location: ~/.fern/src/cpp Cache is up to date
Clear Cache Clearing Fern Web Cache ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Web cache cleared successfully Cache will be recreated automatically on next web build
This removes the precompiled library. The next web build will rebuild it automatically.
Rebuild Cache Rebuilding Fern Web Cache ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Cleared existing cache Building Fern web library (this may take a moment )... Compiling Fern sources... Creating static library... Web cache rebuilt successfully Cache location: ~/.fern/cache/web/libfern_web.a
Forces an immediate rebuild of the cache.
Cache Status Details The status command shows:
Cache location - Directory containing cached filesLibrary file - Precompiled library filenameSize - File size in MBLast modified - When cache was last built
Source location - Fern framework source directoryUp to date status - Whether cache matches source
Cache States
Cache available and up to date
Web cache is available Cache is up to date
Everything is working optimally. Web builds will be fast.
Web cache is available Cache may be outdated (source files newer than cache ) Cache will be automatically rebuilt on next web build
The cache will be rebuilt automatically on your next web build.
Web library cache not found Expected file: ~/.fern/cache/web/libfern_web.a Cache will be created automatically on first web build
Normal on first use. Cache will be created when you build for web.
Web cache directory does not exist Expected location: ~/.fern/cache/web Cache will be created automatically on first web build
The cache directory will be created automatically. When to Clear Cache Clear the cache when:
Fern is updated - After installing a new version of FernBuilds fail mysteriously - Cache corruption can cause build issuesTesting changes - When developing Fern framework itselfDisk space needed - Cache uses ~2-3 MB
When Cache Rebuilds Automatically The cache automatically rebuilds when:
Cache doesn’t exist
Fern source files are newer than cache
Running fern fire -p web or fern prepare web
You don’t usually need to manually rebuild.
Without Cache fern fire -p web # First build: ~30 seconds # Subsequent builds: ~30 seconds (everything recompiles)
With Cache fern fire -p web # First build: ~30 seconds (creates cache) # Subsequent builds: ~5 seconds (uses cache)
Speed improvement: 6x faster! Cache Contents The cache contains:
~/.fern/cache/web/ └── libfern_web.a # Precompiled Fern library (static archive)
During rebuild, temporary files are created:
~/.fern/cache/web/ ├── obj_0.o # Temporary object files ├── obj_1.o ├── ... └── libfern_web.a # Final library (temp files deleted)
Cache Location ~/.fern/cache/web/libfern_web.a
Precompiled Fern web library
Troubleshooting
Web build fails after Fern update
fern fire -p web # Error: linking failed
Solution: Clear and rebuild the cache: fern web-cache clear fern fire -p web # Rebuilds cache automatically
fern web-cache rebuild # Error: Fern source not found
Solution: Reinstall Fern: cd /path/to/fern ./install.sh fern web-cache rebuild
Slow web builds even with cache
Check cache status: If cache is outdated or missing, rebuild:
Emscripten errors during rebuild
fern web-cache rebuild # Error: emcc: command not found
Solution: Activate Emscripten: source ~/emsdk/emsdk_env.sh fern web-cache rebuild
Build Process Detail Without Cache emcc main.cpp \ src/core/ * .cpp \ src/graphics/ * .cpp \ src/text/ * .cpp \ src/font/ * .cpp \ src/ui/ ** / * .cpp \ src/platform/web_renderer.cpp \ # ... all Fern sources (~50 files) -o output.html
Every file is compiled each time.
With Cache # Cache creation (once) emcc -c src/core/ * .cpp ... # Compile Fern to .o files emar rcs libfern_web.a * .o # Create static library # Each build (fast) emcc main.cpp libfern_web.a -o output.html
Only your code is compiled; Fern is pre-compiled.
Advanced Usage Manual Cache Management You can manually manage the cache directory:
# Check cache size du -sh ~/.fern/cache/web # Remove old object files rm ~/.fern/cache/web/ * .o # Backup cache cp ~/.fern/cache/web/libfern_web.a ~/backup/ # Restore cache cp ~/backup/libfern_web.a ~/.fern/cache/web/
Multiple Fern Versions If you have multiple Fern installations:
# Each Fern installation uses the same cache # Clear cache when switching versions fern web-cache clear
Development Workflow When developing Fern framework:
# Make changes to Fern source vim src/core/renderer.cpp # Rebuild cache to test fern web-cache rebuild # Test with your project cd ~/my_app fern fire -p web