popovychjob

Built the same thing with a different tradeoff — Canvas API instead of WASM — so a couple of notes from that side.

The privacy claim is stronger than you're stating it. Canvas re-encoding doesn't just avoid the upload, it strips EXIF as a side effect: GPS coordinates, device model, timestamps all disappear because you're drawing pixels to a new surface and calling toBlob(). For photos straight off a phone that's often the actual risk, not the upload. Worth saying explicitly — users don't know their images carry location data.

Two things Canvas gets wrong that WASM probably saves you from, and I'd be curious which side you landed on:

- Canvas is sRGB by default. An image tagged Display P3 gets silently converted on draw, so saturated colors shift. You need colorSpace: 'display-p3' on getContext to preserve it, and support isn't universal. - toBlob() quality is browser-dependent for JPEG. Quality 0.8 in Chrome and Safari are not the same file. Fine for "make it smaller", not fine if someone is matching a target size.

For HEIC I ended up with a split: Safari decodes it natively through the OS at zero library cost, and Chrome/Firefox lazy-load a WASM libheif build only after a HEIC file is actually detected. Meant the other 95% of visits never download the decoder. If you're already fully WASM you may not care, but the conditional load was worth the complexity for us.