NES games in a GBA cartridge?

I've seen my friend playing with his old GBA handheld and I saw that the games he was playing were Battle City, Contra[...] and some other NES games[contents of the cartridge he was playing].

So how do I play NES games in a GBA handheld?

 

Its one of those fake catdrige.
There's like 4 GBA games,and the rest are NES games.
I have a few of those myself

 

yar, I want to know how to play NES games in a GBA handheld....

do you have to like convert .nes to .gba?

 

Yes, there is an emulator for NES on GBA.

Pocket NES Download

You just have to make a GBA file with NES roms with the program included in the download.
It is very simple to use and there are even ones for GB/GBC as well. It's called Goomba Color. And one for GameGear....I forget what that's called

It is basically a massive amount of NES games in a single GBA file. I have 26 or so NES games in my PocketNES.GBA file.

 

Thanks, I'll try it out