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Why does TypeScript fail to infer a callback parameter in a union when the discriminating property is an array literal?

TypeScript struggles to infer callback parameters in unions with array literals, affecting type safety.

Steady
Signal score
49
Sources
5
agreeing on typescript
Trajectory
↑ Accelerating
7-day est. ~44

Why this scored 49

every term, weighted
Velocity+10.0 / 40

Engagement gained per hour since the last capture, against the fastest item on its own source

Acceleration+11.5 / 25

Whether that velocity is itself speeding up, as a per-hour rate

Cross-source spread+20.0 / 25

How many independent communities are talking about the same entity

Recency+8.4 / 10

Decays to zero over 14 days

Saturation penalty−0.6 / 30

Subtracted once something is big and old — we rank what's next, not what's peaked

Composite49.2

Weights are hand-tuned, not learned — we're calibrating them against realized trends as history accumulates. On a topic's first sighting there's no previous reading to compare against, so acceleration starts from a neutral prior rather than a measurement, and velocity falls back to engagement over its whole lifetime until a second reading exists. Full methodology

Outlook

low confidence · estimate, not a guarantee

7-day

~44

range 3–56

14-day

~46

range 2–60

30-day

~47

range 0–66

Signal history

7-day window (free)
2968

projected trajectory (estimate, not a guarantee)

Entities

typescript
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