TypeError: Cannot set property 'checked' of null for CheckBox

Question

document.getElementById("cbox0").checked = true;

I am using this statement to auto check a checkbox but i get TypeError: Cannot set property 'checked' of null for CheckBox this error. I have tried to use if statement to check if its not a null but it also give me the same error.

jsp+='<input id="cbox'+index+'" type="checkbox" name="compare" value="'+rightCard.oid+'" onchange="myFunction('+index+')"><label for="cboxCard'+index+'">&nbsp;</label>';

Answer 1

There could be 2 possible problems.

1. There is no checkbox with the id as cbox0. Hence, getElementById returns null, leading to your error
2. Your JavaScript is executed before your checkbox is loaded into the DOM. You can solve this by wrapping your code inside a DOMContentLoaded event listener, like this

document.addEventListener("DOMContentLoaded", function() {
  document.getElementById("cbox0").checked = true;
});

<input id="cbox0" type="checkbox" name="compare" value="test">

Note that the snippet above works even without the event listener on StackOverflow. That's probably because StackOverflow's snippet runs it's JavaScript similar to what I've written.

Answer 2

wrap your code within an onload event.