How do I make a gun project a particle?

I am trying to make a gun, but I dont want an actual bullet to come out like some tutorials say. I did that, and I dont like it. it barely works for me, and it doesn't look good. Instead, I would like to simply project a particle directly in front of the main camera (where my crosshair is). Ive been looking forever, and I dont want to use the machinegun.js found in the fps tutorial) How would I go about doing this? (javascript please)

Thanks in advance :)