FPS tutorial projectile scripting error

For the projectile Weaponscript in the FPS tutaorial I typed the following code which, as far as I can tell is correct but I keep getting this error: Assets/Weaponscripts/Projectile.js(5,38): BCE0005: Unknown identifier: 'collision'.

This is the script-

var explosion : GameObject;

function OnCollisionEnter( Collision : Collision ) { var contact : ContactPoint = collision.contacts[0];

var rotation = Quaternion.FromToRotation( Vector3.up, contact.normal ); var instantiatedExplosion : GameObject = Instantiate( explosion, contact.point, rotation );

Destroy( gameObject );

}