Question
Is there a book called the "Sefer ha-Yashar" (Joshua 10:13 and 2 Samuel 1:18)?
Answer
A book called the Sefer ha-Yashar that expands on the Biblical narratives, attributed to Josephus, was published in Venice in 1625, and many times since. It definitely isn't the lost Sefer ha-Yashar which is mentioned in the Bible.