* small fixes to stopwatch codesandbox
noticed that the explanation for the first stopwatch codesandbox mentions "update the time every 10 milliseconds" so updated the codesandbox to reflect that
also there's a small nuanced bug in the second stopwatch codesandbox where each call to `handleStart()` sets a new interval without checking if there's already one ongoing.
Ie: If the user accidentally double clicks the start button, they set two intervals for updating `now` every 10ms and then intervalRef only retains the second interval ID. Thus, it's impossible to actually stop the timer because `handleStop()` will only clear the latest set interval while the original one will keep executing.
* Update referencing-values-with-refs.md
* Update referencing-values-with-refs.md
* Update referencing-values-with-refs.md
Co-authored-by: dan <dan.abramov@gmail.com>