The Book of Jasher or Sefer ha-Yashar, Translated from the Original Hebrew to English

The Book of Jasher is the normal English name (used by e.g. the King James Bible) of a work known in the original Hebrew as Sefer haYashar, (ספר הישר; also transliterated Sēper haiYāšār). It is the best-known of several "Lost books of the Old Testament", books referenced in the Hebrew Bible of which no copies are known to exist. The original Hebrew translates as "Book of the Upright".

Joshua 10:13 states:

And the Sun stood still, and the Moon stayed,
until the people had avenged themselves on their enemies.

Is this not written in the Book of the Upright (Sēper haiYāšār)?

2 Samuel 1:18 states:

To teach the Sons of Judah the use of the bow; behold it is written in the Book of the Upright (Sēper haiYāšār)