Checkbox is checked but returns false

I would like to use some JS to perform a function if a checkbox is checked. However, my input field checkbox keeps returning false when it’s checked and I can’t understand why.

Here’s the HTML:

<input id="option_service_desk" type="checkbox"/>

Here’s the JS:

if (document.getElementById('option_service_desk').checked)
 { 
 console.log('service 247 checked');
} else {
 console.log("service 247 not checked");
}

I’ve tried checking in the console and indeed, it’s returning as false, even though it is checked on the screen.