Triggering action in other player

[i8bit]

I am trying to stay away from Serverside functions.

How would I trigger an action in a Weapon on a player in front of me..

For example:
Player swinging sword

PHP Code:

//#CLIENTSIDE
function onKeyPressed(code, key){
 if (key == "s"){
  setAni("sword", NULL);
  //trigger action "onHit" in the weapon "DamageSystem" to the player right in front
 }
} 


PHP Code:

//Damage system
//#CLIENTSIDE
function onHit(){
 //what ever actions I want to take place
}