Question

I want to run my function at the first time immediately (without timeout) so I do this:

setInterval(function(){
    alert("Boo");
}(), 1000);

The function executed at first time but in next intervals, nothing happened. Why?

Answer 1

The better question is, what are you actually trying to achieve ?

You don’t return anything from the self-invoking function, so it will return the undefined value implicitly, which is passed over to setTimeout. After the initial call, the line would look like

setInterval(undefined, 1000); 

which obviously, makes no sense and won’t continue calling anything.

You either need to to return another function from your self-invoking function, or just don’t use a self-invoking function and just pass over the function reference.

---

Update:

You updated your question. If you want to run a function “once” on init and after that use it for the interval, you could do something like

setInterval((function() {
    function loop() {
        alert('Boo');
    };

    loop();
    return loop;
}()), 1000);