How do I determine if a checkbox is checked?

javascript html checkbox
Sean picture Sean · Jan 21, 2011 · Viewed 369.5k times · Source

For some reason, my form does not want to get the value of a checkbox... I am not sure if it is my coding or not, but when I try and alert() the value, I get undefined as a result. What do I have wrong?

<head>
  <script>
    var lfckv = document.getElementById("lifecheck").checked
    function exefunction(){
      alert(lfckv);
    }
  </script>
</head>
<body>
  <label><input id="lifecheck" type="checkbox" >Lives</label>
</body>

EDIT

I tried changing it to this

function exefunction() {
    alert(document.getElementById("lifecheck").checked);
}

But now it doesn't even want to execute. What's going wrong?

Answer

Elian Ebbing picture Elian Ebbing · Jan 21, 2011

Place the var lfckv inside the function. When that line is executed, the body isn't parsed yet and the element "lifecheck" doesn't exist. This works perfectly fine:

function exefunction() {
  var lfckv = document.getElementById("lifecheck").checked;
  alert(lfckv);
}
<label><input id="lifecheck" type="checkbox" >Lives</label>
<button onclick="exefunction()">Check value</button>

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