The 19-year-old has featured six times for Rangers but has made just one league start.
Cobblers boss Ian Sampson told the club's website: "I saw Josh play a year or two back and was very impressed and have kept tabs on him ever since. I know he is very highly rated and I would like to thank Neil Warnock for allowing us to borrow him."
He added: "He plays on the right-wing, he is very quick and delivers a good cross. He can also play at full-back or up front and I think he will add to and improve the squad."
The youngster, who played twice while on loan at AFC Wimbledon last season, is available for Saturday's trip to Macclesfield.
Source: BBC Sport
Source: BBC Sport