Priority hints
Slap yourself if
You think priority hints force the browser to load things faster or assume they override the browser’s scheduler.
Why this exists
Because priority hints are widely misunderstood as commands instead of suggestions, leading teams to add them everywhere and accidentally make loading worse.
Mental model
Priority hints bias the browser’s request scheduler. They do not bypass dependency graphs, bandwidth limits, or protocol constraints.
- The browser assigns internal priorities to requests based on heuristics.
- Priority hints adjust those heuristics slightly for specific resources.
- The scheduler still respects dependencies, connection limits, and protocol behavior.
- Hints may be ignored if they conflict with higher-confidence signals.
- Marking everything as high priority.
- Assuming fetchpriority guarantees earlier download.
- Using hints to fix fundamentally bad loading order.
- Ignoring protocol-level prioritization (HTTP/2, HTTP/3).
Priority hints influence the browser’s request prioritization heuristics but do not override dependency graphs or guarantee ordering.
- Calls them commands.
- Claims they replace preload.
- Ignores scheduler heuristics.
- Assumes consistent behavior across browsers.
Deep dive
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