Can't get HTML checkbox value in JavaScript

Question

I'm trying to get ASP.NET checkbox value which can be user input or retrieved from database. But each time it's showing this error message

0x800a138f - JavaScript runtime error: Unable to get property 'value' of undefined or null reference

My HTML code:

<input type="checkbox" id="myCheck" data-member="IsSubGroupNecessary" data-label="" data-provider="checkbox" onchange="IsSubGroupNeeded();"/>

JavaScript Code:

function IsSubGroupNeeded() {
    var Subgrp = document.getElementById('<%=myCheck.ClientID%>').checked;
    if (Subgrp == true) {
        loadgrdSubgroupItem();
    }
};

Update: The error issue is solved. But I want to call loadgrdSubgroupItem function when checkbox value is true whether it is user input or retrieved from database. How to do it?

It seems that error is thrown somewhere else, can you attach debugger in browser and check where this exception is thrown ? — Michael
– Michael, Commented Feb 10, 2016 at 10:45
@Amey Deshpande it doesn't fire the error but doesn't work too. — Mimi
– Mimi, Commented Feb 10, 2016 at 10:49
Original Question was for ASP.NET checkbox, approved edit is now HTML checkbox.What the hell. — Hemal
– Hemal, Commented Feb 10, 2016 at 10:50
@mimi: re: update - if you have a follow up question ask a new one :-) — NikolaiDante
– NikolaiDante, Commented Feb 10, 2016 at 11:10

NikolaiDante · Accepted Answer · 2016-02-10 10:48:23Z

1

Your rendered HTML has an id of myCheck so you should be able to:

function IsSubGroupNeeded() {
    var Subgrp = document.getElementById('myCheck').checked;
    if (Subgrp == true) {
        loadgrdSubgroupItem();
    }
};

Without the need for the server side call.

(I assume that you have ClientIDMode="Static" on your asp.net markup)

edited Feb 10, 2016 at 10:48

answered Feb 10, 2016 at 10:46

NikolaiDante

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2 Comments

Hemal Over a year ago

# needed?I think no hash needed

NikolaiDante Over a year ago

Yes, I think I may have gone to jquery by accident.

Nithya Chandrashekaran · Accepted Answer · 2016-02-10 10:47:43Z

1

Since checkbox is not an ASP control , you can do as

var subgrp = document.getElementById('myCheck').checked

answered Feb 10, 2016 at 10:47

Nithya Chandrashekaran

1165 bronze badges

Comments

Zaki · Accepted Answer · 2016-02-10 10:53:33Z

1

You need to pass the name of the control only to getElementById to find that element here is an example:

<html>
<head>
<script>
function IsSubGroupNeeded() {
var Subgrp = document.getElementById('myCheck').checked;
   alert(Subgrp)

};
</script>
</head>
<body>
<input type="checkbox" id="myCheck" data-member="IsSubGroupNecessary" data-label="" data-provider="checkbox" onchange="IsSubGroupNeeded();"/>
</body>
</html>

edited Feb 10, 2016 at 10:53

answered Feb 10, 2016 at 10:48

Zaki

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Comments

Hemal · Accepted Answer · 2016-02-10 10:47:07Z

0

It should be

var Subgrp = <%=myCheck.Checked%>;

If checkbox is HTML

function IsSubGroupNeeded() {
    var Subgrp = document.getElementById('myCheck').checked;
    if (Subgrp == true) {
        loadgrdSubgroupItem();
    }
};

edited Feb 10, 2016 at 10:47

answered Feb 10, 2016 at 10:42

Hemal

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3 Comments

Michael Over a year ago

Wouldn't this be set on form rendering and never ever change on checkbox clicks?

Hemal Over a year ago

OP told it is an ASP.NET checkbox, so <%=myCheck.Checked%>; will work perfectly.

Hemal Over a year ago

I oppose this downvote. Can the person explain downvote?

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