Streaming fetch response handling
Slap yourself if
You think fetch resolves when the response is ‘ready’ and streaming is just reading chunks in a loop.
Why this exists
Streaming fetch response handling exists because waiting for full responses wastes time, memory, and user attention. The browser can deliver bytes progressively, but only if your code cooperates with streaming semantics, backpressure, and cancellation.
Mental model
A fetch response is a live data source, not a blob. Handling it correctly means coordinating consumption rate, partial parsing, and lifecycle — not just calling response.json().
- fetch resolves once headers are available, not when the body is complete.
- The response body is exposed as a ReadableStream.
- Chunks arrive over time and may vary in size and timing.
- Consumption rate influences buffering and memory pressure.
- Calling response.json() and accidentally buffering the entire body.
- Assuming chunk boundaries align with logical data boundaries.
- Ignoring backpressure signals when processing chunks.
- Forgetting to cancel streams on navigation or user abort.
Streaming fetch response handling means consuming the response body incrementally via streams, coordinating parsing, backpressure, and cancellation instead of buffering the entire payload upfront.
- Large responses parsed with response.text() or response.json()
- Custom parsers that assume fixed chunk sizes
- No AbortController tied to the fetch lifecycle
- Streaming used without measuring memory impact
Deep dive
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