[Bible Knowledge Commentary, Old Testament, Walvoord & Zuck, Victor Books, USA, 1987, Donald K. Campbell, pp. 325]:

"The Bible does not identify the author of this book. Many liberal scholars consider it a composite of the documents which supposedly underline the Pentateuch, but a strong case can be made for unity of composition by a single author (e.g., Gleason L. Archer, A Survey of Old Testament Introduction. Chicago: Moody Press, 1964, pp. 252-3). Any discussion of authorship should keep the following matters in mind: (1) And eyewitness wrote many parts of the book (cf. the 'we' and 'us' references in 5:1, 6; and the vivid descriptions of the sending of the spies, the crossing of the Jordan, the capture of Jericho. the battle of Ali, etc.). (2) An early authorship is required by internal evidence (Rahab was alive at the time of writing [6:25]; the Jebusites still inhabited Jerusalem [15:63]; Canaanite cities are mentioned by archaic names, such as Baalah for Kiriath Jearim and Kiriath Arba for Hebron [15:9, 13]; Tyre had not yet conquered Sidon which it did in the 12th century [13:4-6]; the philistines were not a national menace to Israel as they became after their invasion about 1200 B.C.). (3) Joshua had written parts of the book (cf. 8:32; 24:26). (4) Other parts of the book were clearly written after Joshua's death (cf. 24:29-30 - the record of his death; 15:13-14 - Caleb's conquest of Hebron [also recorded in Jud. 1:1, 10, 20]; Josh. 15:1519 - Othniel's conquest of Debir [also recorded in Jud. 17-18]). In light of these factors many evangelical scholars ascribe the book to Joshua himself as the main author with minor additions made by Eleazar the high priest and his son Phinehas."