olark('api.chat.onOperatorsAway', function() {
	// Your callback function
});

Notes

Whenever all operators are offline, the given callback will be triggered.

Indicate your operators are offline

Show a red icon whenever you have operators available to chat:

<!-- HTML element to show chatbox status -->
<div id="chat-indicator">Live chat</div>

<style type="text/css">

    /* Operators available */
    .green-icon {
        background-color: green;
    }

    /* Operators offline */
    .red-icon {
        background-color: red;
    }

</style>

<script>
olark('api.chat.onOperatorsAvailable', function() {

    // Identify the element, and give it a class name
    document.getElementById('chat-indicator').className = 'green-icon';

});
olark('api.chat.onOperatorsAway', function() {

    // Identify the element, and give it a class name
    document.getElementById('chat-indicator').className = 'red-icon';

});
</script>

Here is an example of what it might look like with a little styling. In this example, we also added selectors to change the text as well as the color.

<style type="text/css">

    /* Operators available */
    .green-icon {
    background-color: green;
    }
    .green-icon::after {
        content: ": on";
    }

    /* Operators offline */
    .red-icon {
    background-color: red;
    }
    .red-icon::after {
        content: ": off";
    }
</style>

Screenshot of API call on Operators Available 2

Please note: This call will only fire if an operator’s state changes. It cannot be queried.