bind ()

<!DOCTYPE html>
<html>
<head>
    <title>Test</title>
</head>
<body>
<div id="lightswitch">lightswitch <- click on it</div>

<script>

var lightbulb = {
        toggle: function toggle() {
            this.isOn = !this.isOn;
            return this.isOn;
        },
        isOn: false
    },
    toggle = lightbulb.toggle,
    lightswitch = document.getElementById('lightswitch');

    lightswitch = document.getElementById('lightswitch');

    lightswitch.addEventListener('click', function(){
        alert(lightbulb.toggle);
    }, false);
</script>

</body>
</html>