what are #pragma?

seems stupid but...

I look around and oly found for c and c++

in unity, I see they in js someone could explain me #pragma strict #pragma implicit #pragma downcast

1. what are?

2. what they do?

3. when do use?

4. there is others pragma?

I found this in a sample project, are really needed?

 #pragma strict
 #pragma implicit
 #pragma downcast
 
 class FadeLight extends MonoBehaviour
 {
  public var delay : float;
  public var fadeTime : float;
  
  private var fadeSpeed : float;
  private var intensity : float;
  private var color : Color;
  new pre
  function Start()new pre
  {
  if(light == null)
  {
  Destroy(this);
  return;
  }
  new pre
  intensity = light.intensity;
  
  
  fadeTime = Mathf.Abs(fadeTime);
  
  if(fadeTime > 0.0)
  {
  fadeSpeed = intensity / fadeTime;
  }
  else
  {
  fadeSpeed = intensity;
  }
  //alpha = 1.0;
  }
  
  function Update()
  {
  if(delay > 0.0)
  {
  delay -= Time.deltaTime;
  }
  else if(intensity > 0.0)
  {
  intensity -= fadeSpeed * Time.deltaTime;
  light.intensity = intensity;
  }
  }
 }