kak ispolzovat html checkbox

1<input type="checkbox" onclick="checkFluency()"  id="fluency" checked />

1function checkFluency()
2{
3  var checkbox=document.getElementById('fluency');
4  if(checkbox.checked!=true)
5  {
6    alert("you need to be fluent in English to apply for the job");
7  }
8}
9