How do I set a live timer?

Unity Engine
1

I want to make an object last for only 3 seconds, how would I make a code that destroys it after 3 seconds? (javascript plz)

2 
var timeAlive : float = 0f;

function Update () {
		// Destoy after 3 sec
		 timeAlive  = timeAlive + Time.deltaTime;
		if (timeAlive >= 3){
                    Destroy(gameObject);
                }
	}
3

There is example in javascript:

4

You might also want to invoke a destroy function of your own making.
Destroy(gameObject, 3) would also work, but you can’t cancel it.

The below code also works, in addition to being able to use CancelInvoke();

Invoke (DestroyMyObject, 3);

DestroyMyObject()
{
Destroy(gameObject);
}
5

Well, this would work too:

function Start () {
  Destroy (gameObject, 3);
}