setInterval() only running function once

Question

I want to periodically query a PHP script for new messages. To do so, I'm using the setInterval() function and AJAX.

$(document).ready(function(){

    var queryInterval = 1000; /* How fast we query for new messages */

    setInterval(getMessages(), queryInterval);

    function getMessages() {
        console.log("tick");
    }

});

However, when I look at the Javascript console, I'm only seeing "tick" once. I've made sure that the console doesn't ignore any more logs of the same strings, so if the code was working properly it should show "tick" in the console every second.

Anyone know what could be going wrong here?

Answer 1

Change:

setInterval(getMessages(), queryInterval);

To:

setInterval(getMessages, queryInterval);

Answer 2

Actually, setInterval isn't running getMessages at all (not even once). setInterval expects a reference to a function, but you're executing the getMessages function immediately and passing its return value to setInterval (which is undefined). That's what the parens after getMessage do.

Pass a reference to setInterval like this:

setInterval(getMessages, queryInterval);

If this is the only place that getMessages is used, then you could also write it like this:

setInterval(function() {
    console.log("tick");
}, queryInterval);