The 19-year-old winger has appeared three times for the West London side since breaking into the first team towards the end of last season.
"Josh has made significant progress in a short period of time," Bees manager Mark Warburton told the club website.
Brentford earned promotion to the second tier by finishing second in League One in 2013-14.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Manchester CityMan City | 3 | 3 | 0 | 0 | 9 | 2 | 7 | 9 |
| 2 | Liverpool | 3 | 3 | 0 | 0 | 7 | 0 | 7 | 9 |
| 3 | Brighton & Hove AlbionBrighton | 3 | 2 | 1 | 0 | 6 | 2 | 4 | 7 |
| 4 | Arsenal | 3 | 2 | 1 | 0 | 5 | 1 | 4 | 7 |
| 5 | Newcastle UnitedNewcastle | 3 | 2 | 1 | 0 | 4 | 2 | 2 | 7 |
| 6 | Brentford | 3 | 2 | 0 | 1 | 5 | 4 | 1 | 6 |
| 7 | Aston Villa | 3 | 2 | 0 | 1 | 4 | 4 | 0 | 6 |
| 8 | Bournemouth | 3 | 1 | 2 | 0 | 5 | 4 | 1 | 5 |
| 9 | Nottingham ForestNott'm Forest | 3 | 1 | 2 | 0 | 3 | 2 | 1 | 5 |
| 10 | Tottenham HotspurSpurs | 3 | 1 | 1 | 1 | 6 | 3 | 3 | 4 |
| 11 | Chelsea | 3 | 1 | 1 | 1 | 7 | 5 | 2 | 4 |
| 12 | Fulham | 3 | 1 | 1 | 1 | 3 | 3 | 0 | 4 |
| 13 | West Ham UnitedWest Ham | 3 | 1 | 0 | 2 | 4 | 5 | -1 | 3 |
| 14 | Manchester UnitedMan Utd | 3 | 1 | 0 | 2 | 2 | 5 | -3 | 3 |
| 15 | Leicester CityLeicester | 3 | 0 | 1 | 2 | 3 | 5 | -2 | 1 |
| 16 | Crystal Palace | 3 | 0 | 1 | 2 | 2 | 5 | -3 | 1 |
| 17 | Ipswich TownIpswich | 3 | 0 | 1 | 2 | 2 | 7 | -5 | 1 |
| 18 | Wolverhampton WanderersWolves | 3 | 0 | 1 | 2 | 3 | 9 | -6 | 1 |
| 19 | Southampton | 3 | 0 | 0 | 3 | 1 | 5 | -4 | 0 |
| 20 | Everton | 3 | 0 | 0 | 3 | 2 | 10 | -8 | 0 |
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