Function

watchedFraction

watchedFraction(positionSeconds: number | null, durationSeconds: number): number
How much of a lesson the learner has watched, as a share of its runtime.
Parameters
- positionSeconds: number | null
  The stored position, or null when nothing is saved
- durationSeconds: number
  The lesson's length; <= 0 is treated as unknown
Returns number
A number in [0, 1]; 0 whenever the inputs cannot be divided
Remarks
A presentation policy, like isPositionResumable: it exists so a progress bar can be drawn, and deliberately lives outside the hexagon. Range and finiteness of a persisted position are the PlaybackPosition value object's job; this function additionally tolerates whatever a detached player or a hand-edited storage entry hands it, because a bar is never worth a thrown error.

A lesson with no runtime — every reading lesson — has no watched fraction rather than an infinite one.
Example
```
watchedFraction(240, 600); // 0.4
watchedFraction(700, 600); // 1   — clamped
watchedFraction(null, 600); // 0
```
- Defined in lib/watch-progress/watch-progress.ts:81