The Book of Jasher: Referred to in Joshua & Second Samuel

The Book of Jasher covers the Mosaic period of the Bible presented in Genesis, Exodus, Numbers, Deuteronomy, and Joshua in greater detail and with explanations not found in the present Old Testament Documents. This apocryphal book of the Bible has been considered by some to be the original beginning to the Bible and is referenced in both the Book of Joshua and the Second Book of Samuel. Is not this written in the Book of Jasher?-Joshua, X. 13. Behold it is written in the Book of Jasher.-II. Samuel, I. 18