setInterval repeat 3 time and kill

You'll need to use either a global variable, or a closure.

In your example, simply doing:

function texte(){
    var idAnim = setInterval(function(a,y,c){
      console.log(a,y);
      compteurAnim++;
      if (compteurAnim >= a.length) { clearInterval(idAnim);}
    }, 100, mot, 0);
    mot+="foo";
}

will work. idAnim will then be defined in the function each time it is called, and the setInterval callback will be able to reference it.

As I think you figured out, in idAnim = setInterval( anim, 500, "foo", 0, idAnim); the setInterval has to be called before idAnim is set to the correct return value, so you'll always get the wrong answer in there.