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Checkbox not returning correct value [duplicate]

I need to check the checked property of a checkbox and perform an action based on the checked property using jQuery.
For example, if the age checkbox is checked, then I need to show a textbox to enter age, else hide the textbox.
But the following code returns false by default:
if ($('#isAgeSelected').attr('checked')) {
$("#txtAge").show();
} else {
$("#txtAge").hide();
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="checkbox" id="isAgeSelected"/>
<div id="txtAge" style="display:none">
Age is selected
</div>
How do I successfully query the checked property?

How do I successfully query the checked property?
The checked property of a checkbox DOM element will give you the checked state of the element.
Given your existing code, you could therefore do this:
if(document.getElementById('isAgeSelected').checked) {
$("#txtAge").show();
} else {
$("#txtAge").hide();
}
However, there's a much prettier way to do this, using toggle:
$('#isAgeSelected').click(function() {
$("#txtAge").toggle(this.checked);
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="checkbox" id="isAgeSelected"/>
<div id="txtAge" style="display:none">Age is something</div>

Use jQuery's is() function:
if($("#isAgeSelected").is(':checked'))
$("#txtAge").show(); // checked
else
$("#txtAge").hide(); // unchecked

Using jQuery > 1.6
<input type="checkbox" value="1" name="checkMeOut" id="checkMeOut" checked="checked" />
// traditional attr
$('#checkMeOut').attr('checked'); // "checked"
// new property method
$('#checkMeOut').prop('checked'); // true
Using the new property method:
if($('#checkMeOut').prop('checked')) {
// something when checked
} else {
// something else when not
}

jQuery 1.6+
$('#isAgeSelected').prop('checked')
jQuery 1.5 and below
$('#isAgeSelected').attr('checked')
Any version of jQuery
// Assuming an event handler on a checkbox
if (this.checked)
All credit goes to Xian.

I am using this and this is working absolutely fine:
$("#checkkBoxId").attr("checked") ? alert("Checked") : alert("Unchecked");
Note: If the checkbox is checked it will return true otherwise undefined, so better check for the "TRUE" value.

Use:
<input type="checkbox" name="planned_checked" checked id="planned_checked"> Planned
$("#planned_checked").change(function() {
if($(this).prop('checked')) {
alert("Checked Box Selected");
} else {
alert("Checked Box deselect");
}
});
$("#planned_checked").change(function() {
if($(this).prop('checked')) {
alert("Checked Box Selected");
} else {
alert("Checked Box deselect");
}
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<input type="checkbox" name="planned_checked" checked id="planned_checked"> Planned

Since jQuery 1.6, the behavior of jQuery.attr() has changed and users are encouraged not to use it to retrieve an element's checked state. Instead, you should use jQuery.prop():
$("#txtAge").toggle(
$("#isAgeSelected").prop("checked") // For checked attribute it returns true/false;
// Return value changes with checkbox state
);
Two other possibilities are:
$("#txtAge").get(0).checked
$("#txtAge").is(":checked")

This worked for me:
$get("isAgeSelected ").checked == true
Where isAgeSelected is the id of the control.
Also, #karim79's answer works fine. I am not sure what I missed at the time I tested it.
Note, this is answer uses Microsoft Ajax, not jQuery

If you are using an updated version of jquery, you must go for .prop method to resolve your issue:
$('#isAgeSelected').prop('checked') will return true if checked and false if unchecked. I confirmed it and I came across this issue earlier. $('#isAgeSelected').attr('checked') and $('#isAgeSelected').is('checked') is returning undefined which is not a worthy answer for the situation. So do as given below.
if($('#isAgeSelected').prop('checked')) {
$("#txtAge").show();
} else {
$("#txtAge").hide();
}

Use:
<input type="checkbox" id="abc" value="UDB">UDB
<input type="checkbox" id="abc" value="Prasad">Prasad
$('input#abc').click(function(){
if($(this).is(':checked'))
{
var checkedOne=$(this).val()
alert(checkedOne);
// Do some other action
}
})
This can help if you want that the required action has to be done only when you check the box not at the time you remove the check.

You can try the change event of checkbox to track the :checked state change.
$("#isAgeSelected").on('change', function() {
if ($("#isAgeSelected").is(':checked'))
alert("checked");
else {
alert("unchecked");
}
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="checkbox" id="isAgeSelected" />
<div id="txtAge" style="display:none">
Age is selected
</div>

Using the Click event handler for the checkbox property is unreliable, as the checked property can change during the execution of the event handler itself!
Ideally, you'd want to put your code into a change event handler such as it is fired every time the value of the check box is changed (independent of how it's done so).
$('#isAgeSelected').bind('change', function () {
if ($(this).is(':checked'))
$("#txtAge").show();
else
$("#txtAge").hide();
});

I ran in to the exact same issue. I have an ASP.NET checkbox
<asp:CheckBox ID="chkBox1" CssClass='cssChkBox1' runat="server" />
In the jQuery code I used the following selector to check if the checkbox was checked or not, and it seems to work like a charm.
if ($("'.cssChkBox1 input[type=checkbox]'").is(':checked'))
{ ... } else { ... }
I'm sure you can also use the ID instead of the CssClass,
if ($("'#cssChkBox1 input[type=checkbox]'").is(':checked'))
{ ... } else { ... }
I hope this helps you.

I believe you could do this:
if ($('#isAgeSelected :checked').size() > 0)
{
$("#txtAge").show();
} else {
$("#txtAge").hide();
}

I decided to post an answer on how to do that exact same thing without jQuery. Just because I'm a rebel.
var ageCheckbox = document.getElementById('isAgeSelected');
var ageInput = document.getElementById('txtAge');
// Just because of IE <333
ageCheckbox.onchange = function() {
// Check if the checkbox is checked, and show/hide the text field.
ageInput.hidden = this.checked ? false : true;
};
First you get both elements by their ID. Then you assign the checkboxe's onchange event a function that checks whether the checkbox got checked and sets the hidden property of the age text field appropriately. In that example using the ternary operator.
Here is a fiddle for you to test it.
Addendum
If cross-browser compatibility is an issue then I propose to set the CSS display property to none and inline.
elem.style.display = this.checked ? 'inline' : 'none';
Slower but cross-browser compatible.

This code will help you
$('#isAgeSelected').click(function(){
console.log(this.checked);
if(this.checked == true) {
$("#txtAge").show();
} else {
$("#txtAge").hide();
}
});

This works for me:
/* isAgeSelected being id for checkbox */
$("#isAgeSelected").click(function(){
$(this).is(':checked') ? $("#txtAge").show() : $("#txtAge").hide();
});

There are many ways to check if a checkbox is checked or not:
Way to check using jQuery
if (elem.checked)
if ($(elem).prop("checked"))
if ($(elem).is(":checked"))
if ($(elem).attr('checked'))
Check example or also document:
http://api.jquery.com/attr/
http://api.jquery.com/prop/

This is some different method to do the same thing:
$(document).ready(function (){
$('#isAgeSelected').click(function() {
// $("#txtAge").toggle(this.checked);
// Using a pure CSS selector
if ($(this.checked)) {
alert('on check 1');
};
// Using jQuery's is() method
if ($(this).is(':checked')) {
alert('on checked 2');
};
// // Using jQuery's filter() method
if ($(this).filter(':checked')) {
alert('on checked 3');
};
});
});
<script src="http://code.jquery.com/jquery-1.9.1.js"></script>
<input type="checkbox" id="isAgeSelected"/>
<div id="txtAge" style="display:none">Age is something</div>

Use this:
if ($('input[name="salary_in.Basic"]:checked').length > 0)
The length is greater than zero if the checkbox is checked.

My way of doing this is:
if ( $("#checkbox:checked").length ) {
alert("checkbox is checked");
} else {
alert("checkbox is not checked");
}

$(selector).attr('checked') !== undefined
This returns true if the input is checked and false if it is not.

You can use:
if(document.getElementById('isAgeSelected').checked)
$("#txtAge").show();
else
$("#txtAge").hide();
if($("#isAgeSelected").is(':checked'))
$("#txtAge").show();
else
$("#txtAge").hide();
Both of them should work.

$(document).ready(function() {
$('#agecheckbox').click(function() {
if($(this).is(":checked"))
{
$('#agetextbox').show();
} else {
$('#agetextbox').hide();
}
});
});

1) If your HTML markup is:
<input type="checkbox" />
attr used:
$(element).attr("checked"); // Will give you undefined as initial value of checkbox is not set
If prop is used:
$(element).prop("checked"); // Will give you false whether or not initial value is set
2) If your HTML markup is:
<input type="checkbox" checked="checked" />// May be like this also checked="true"
attr used:
$(element).attr("checked") // Will return checked whether it is checked="true"
Prop used:
$(element).prop("checked") // Will return true whether checked="checked"

This example is for button.
Try the following:
<input type="button" class="check" id="checkall" value="Check All" /> <input type="button" id="remove" value="Delete" /> <br/>
<input type="checkbox" class="cb-element" value="1" /> Checkbox 1 <br/>
<input type="checkbox" class="cb-element" value="2" /> Checkbox 2 <br/>
<input type="checkbox" class="cb-element" value="3" /> Checkbox 3 <br/>
$('#remove').attr('disabled', 'disabled');
$(document).ready(function() {
$('.cb-element').click(function() {
if($(this).prop('checked'))
{
$('#remove').attr('disabled', false);
}
else
{
$('#remove').attr('disabled', true);
}
});
$('.check:button').click(function()
{
var checked = !$(this).data('checked');
$('input:checkbox').prop('checked', checked);
$(this).data('checked', checked);
if(checked == true)
{
$(this).val('Uncheck All');
$('#remove').attr('disabled', false);
}
else if(checked == false)
{
$(this).val('Check All');
$('#remove').attr('disabled', true);
}
});
});

The top answer didn't do it for me. This did though:
<script type="text/javascript">
$(document).ready(function(){
$("#li_13").click(function(){
if($("#agree").attr('checked')){
$("#saveForm").fadeIn();
}
else
{
$("#saveForm").fadeOut();
}
});
});
</script>
Basically when the element #li_13 is clicked, it checks if the element # agree (which is the checkbox) is checked by using the .attr('checked') function. If it is then fadeIn the #saveForm element, and if not fadeOut the saveForm element.

To act on a checkbox being checked or unchecked on click.
$('#customCheck1').click(function() {
if (this.checked) {
console.log('checked');
} else {
console.log('un-checked');
}
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<input type="checkbox" id="customCheck1">
EDIT: Not a nice programming expression if (boolean == true) though .checked property might return other type variables as well..
It is better to use .prop("checked") instead. It returns true and false only.

I am using this:
<input type="checkbox" id="isAgeSelected" value="1" /> <br/>
<input type="textbox" id="txtAge" />
$("#isAgeSelected").is(':checked') ? $("#txtAge").show() : $("#txtAge").hide();

Though you have proposed a JavaScript solution for your problem (displaying a textbox when a checkbox is checked), this problem could be solved just by css. With this approach, your form works for users who have disabled JavaScript.
Assuming that you have the following HTML:
<label for="show_textbox">Show Textbox</label>
<input id="show_textbox" type="checkbox" />
<input type="text" />
You can use the following CSS to achieve the desired functionality:
#show_textbox:not(:checked) + input[type=text] {display:none;}
For other scenarios, you may think of appropriate CSS selectors.
Here is a Fiddle to demonstrate this approach.

select checkboxes with javascript based on html-5 data attribute

This code is not working:
function autoScrub() {
checkLength = document.querySelectorAll("input[type=checkbox]");
for (var i=0; i < checkLength.length; i++) {
if (checkLength[i].attr('data-z') === 1) {
checkLength[i].checked = true;
}
}
}
Each of my checkboxes has a data-z attribute of either 1 or 0. I'd like to auto-check all of the checkboxes that have a data-z attribute of 1. The code is breaking at if (checkLength[i].attr('data-z') === 1) { as apparently I cannot read the data-attribute this way.
Apart from this the rest of the code works fine. I can use checkLength[i].checked = true; and it will check all of the checkboxes, I just can't reference its data-attribute correctly in an if statement and I'm not sure how to.
Any ideas?
Update
I screwed around with two of the solutions below and finally came up with:
function autoScrub() {
$("input:checkbox").each(function() {
if ($(this).data("z") == 0) {
$(this).prop('checked', true).trigger('change');
}
});
}
and this worked. Thank you everyone for your help!

in jQuery this is one line of code:
$('input[type="checkbox"][data-z="1"]').prop('checked', true);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="checkbox" data-z="1" /><br />
<input type="checkbox" data-z="0" /><br />
<input type="checkbox" data-z="1" /><br />
<input type="checkbox" data-z="1" /><br />
<input type="checkbox" data-z="0" /><br />
EDIT
Just noticed a comment about firing the change event:
$('input[type="checkbox"][data-z="1"]').prop('checked', true).trigger('change');
https://api.jquery.com/trigger/

DOM element nodes don't have an .attr() method. I think you're looking for .getAttribute().
if (checkLength[i].getAttribute('data-z') === "1") {
checkLength[i].checked = true;
}
Also note that your attribute values will be strings, not numbers, so you'll either need to compare to strings as in my edit above, or else compare with ==.
Since you tagged your post with the jQuery tag, I'll add that your code would look like this if you were to go that route:
$("input:checkbox").each(function() {
if ($(this).data("z") == 1)
this.checked = true;
});

if you want to use pure html5 then use HTMLElement.dataset
// el.dataset.dateOfBirth = '1960-10-03'; // set the DOB.
// 'someDataAttr' in el.dataset === false
// el.dataset.someDataAttr = 'mydata';
// 'someDataAttr' in el.dataset === true
(function autoScrub() {
var el = document.querySelectorAll("input[type=checkbox]");
for (var i=0; i < el.length; i++) {
console.log(el[i].dataset.z)
if (el[i].dataset.z === "1") {
console.log(el[i]);
el[i].checked = true;
}
}
})();
<input type=checkbox id=check-1 data-id=111111 data-user=john data-date-of-birth=2jan2010 data-z=1 />
<input type=checkbox id=check-2 data-id=222222 data-user=tambo data-date-of-birth=3feb2011 data-z=2 />
<input type=checkbox id=check-3 data-id=333333 data-user=sandra data-date-of-birth data-z=3 />
<input type=checkbox id=check-4 data-id=444444 data-user=loic data-date-of-birth=4mar2012 data-z=4 />
Note: Accessing the Data
The W3C HTML5 spec has a clear method for collecting data in
JavaScript. Notice that we don’t need the “data-” in front of our
value like with getAttribute; we just call our value name directly.
This access method meets the spec, but like many HTML5 features, it
only works in HTML5 browsers.

check checkbox if another checkbox is checked

I want the checkbox with the value 2 to automatically get checked if the checkbox with the value 1 is checked. Both have the same id so I can't use getElementById.
html:
<input type="checkbox" value="1" id="user_name">1<br>
<input type="checkbox" value="2" id="user_name">2
I tired:
var chk1 = $("input[type="checkbox"][value="1"]");
var chk2 = $("input[type="checkbox"][value="2"]");
if (chk1:checked)
chk2.checked = true;

You need to change your HTML and jQuery to this:
var chk1 = $("input[type='checkbox'][value='1']");
var chk2 = $("input[type='checkbox'][value='2']");
chk1.on('change', function(){
chk2.prop('checked',this.checked);
});
id is unique, you should use class instead.
Your selector for chk1 and chk2 is wrong, concatenate it properly using ' like above.
Use change() function to detect when first checkbox checked or unchecked then change the checked state for second checkbox using prop().
Fiddle Demo

Id should be unique, so that set different ids to your elements, By the way you have to use .change() event to achieve what you want.
Try,
HTML:
<input type="checkbox" value="1" id="user_name1">1<br>
<input type="checkbox" value="2" id="user_name2">2
JS:
var chk1 = $("input[type='checkbox'][value='1']");
var chk2 = $("input[type='checkbox'][value='2']");
chk1.change(function(){
chk2.prop('checked',this.checked);
});

You need to change the ID of one. It is not allowed by W3C standard (hence classes vs ID's). jQuery will only process the first ID, but most major browsers will treat ID's similar to classes since they know developers mess up.
Solution:
<input type="checkbox" value="1" id="user_name">1<br>
<input type="checkbox" value="2" id="user_name_2">2
With this JS:
var chk1 = $('#user_name');
var chk2 = $('#user_name2');
//check the other box
chk1.on('click', function(){
if( chk1.is(':checked') ) {
chk2.attr('checked', true);
} else {
chk2.attr('checked', false);
}
});
For more information on why it's bad to use ID's see this: Why is it a bad thing to have multiple HTML elements with the same id attribute?

The error is probably coming here "input[type="checkbox"]
Here your checkbox is out of the quotes, so you query is looking for input[type=][value=1]
Change it to "input[type='checkbox'] (Use single quote inside double quote, though you don't need to quote checkbox)
http://api.jquery.com/checked-selector/

first create an input type checkbox:
<input type='checkbox' id='select_all'/>
$('#select_all').click(function(event) {
if(this.checked) {
$(':checkbox').each(function() {
this.checked = true;
});
}
});

Check if checkbox is checked with jQuery

How can I check if a checkbox in a checkbox array is checked using the id of the checkbox array?
I am using the following code, but it always returns the count of checked checkboxes regardless of id.
function isCheckedById(id) {
alert(id);
var checked = $("input[#id=" + id + "]:checked").length;
alert(checked);
if (checked == 0) {
return false;
} else {
return true;
}
}

$('#' + id).is(":checked")
That gets if the checkbox is checked.
For an array of checkboxes with the same name you can get the list of checked ones by:
var $boxes = $('input[name=thename]:checked');
Then to loop through them and see what's checked you can do:
$boxes.each(function(){
// Do stuff here with this
});
To find how many are checked you can do:
$boxes.length;

IDs must be unique in your document, meaning that you shouldn't do this:
<input type="checkbox" name="chk[]" id="chk[]" value="Apples" />
<input type="checkbox" name="chk[]" id="chk[]" value="Bananas" />
Instead, drop the ID, and then select them by name, or by a containing element:
<fieldset id="checkArray">
<input type="checkbox" name="chk[]" value="Apples" />
<input type="checkbox" name="chk[]" value="Bananas" />
</fieldset>
And now the jQuery:
var atLeastOneIsChecked = $('#checkArray:checkbox:checked').length > 0;
//there should be no space between identifier and selector
// or, without the container:
var atLeastOneIsChecked = $('input[name="chk[]"]:checked').length > 0;

$('#checkbox').is(':checked');
The above code returns true if the checkbox is checked or false if not.

All following methods are useful:
$('#checkbox').is(":checked")
$('#checkbox').prop('checked')
$('#checkbox')[0].checked
$('#checkbox').get(0).checked
It is recommended that DOMelement or inline "this.checked" should be avoided instead jQuery on method should be used event listener.

jQuery code to check whether the checkbox is checked or not:
if($('input[name="checkBoxName"]').is(':checked'))
{
// checked
}else
{
// unchecked
}
Alternatively:
if($('input[name="checkBoxName"]:checked'))
{
// checked
}else{
// unchecked
}

The most important concept to remember about the checked attribute is
that it does not correspond to the checked property. The attribute
actually corresponds to the defaultChecked property and should be used
only to set the initial value of the checkbox. The checked attribute
value does not change with the state of the checkbox, while the
checked property does. Therefore, the cross-browser-compatible way to
determine if a checkbox is checked is to use the property
All below methods are possible
elem.checked
$(elem).prop("checked")
$(elem).is(":checked")

This is also an idea I use frequently:
var active = $('#modal-check-visible').prop("checked") ? 1 : 0 ;
If cheked, it'll return 1; otherwise it'll return 0.

You can use this code,
if($("#checkboxId").is(':checked')){
// Code in the case checkbox is checked.
} else {
// Code in the case checkbox is NOT checked.
}

As per the jQuery documentation there are following ways to check if a checkbox is checked or not. Lets consider a checkbox for example (Check Working jsfiddle with all examples)
<input type="checkbox" name="mycheckbox" id="mycheckbox" />
<br><br>
<input type="button" id="test-with-checked" value="Test with checked" />
<input type="button" id="test-with-is" value="Test with is" />
<input type="button" id="test-with-prop" value="Test with prop" />
Example 1 - With checked
$("#test-with-checked").on("click", function(){
if(mycheckbox.checked) {
alert("Checkbox is checked.");
} else {
alert("Checkbox is unchecked.");
}
});
Example 2 - With jQuery is, NOTE - :checked
var check;
$("#test-with-is").on("click", function(){
check = $("#mycheckbox").is(":checked");
if(check) {
alert("Checkbox is checked.");
} else {
alert("Checkbox is unchecked.");
}
});
Example 3 - With jQuery prop
var check;
$("#test-with-prop").on("click", function(){
check = $("#mycheckbox").prop("checked");
if(check) {
alert("Checkbox is checked.");
} else {
alert("Checkbox is unchecked.");
}
});
Check Working jsfiddle

I know the OP want jquery but in my case pure JS was the answer so if anyone like me is here and do not have jquery or do not want to use it - here is the JS answer:
document.getElementById("myCheck").checked
It returns true if the input with ID myCheck is checked and false if it is not checked.
Simple as that.

You can try this:
<script>
function checkAllCheckBox(value)
{
if($('#select_all_').is(':checked')){
$(".check_").attr ( "checked" ,"checked" );
}
else
{
$(".check_").removeAttr('checked');
}
}
</script>
<input type="checkbox" name="chkbox" id="select_all_" value="1" />
<input type="checkbox" name="chkbox" class="check_" value="Apples" />
<input type="checkbox" name="chkbox" class="check_" value="Bananas" />
<input type="checkbox" name="chkbox" class="check_" value="Apples" />
<input type="checkbox" name="chkbox" class="check_" value="Bananas" />

You can use any of the following recommended codes by jquery.
if ( elem.checked ) {};
if ( $( elem ).prop( "checked" ) ) {};
if ( $( elem ).is( ":checked" ) ) {};

You can do it simply like;
Working Fiddle
HTML
<input id="checkbox" type="checkbox" />
jQuery
$(document).ready(function () {
var ckbox = $('#checkbox');
$('input').on('click',function () {
if (ckbox.is(':checked')) {
alert('You have Checked it');
} else {
alert('You Un-Checked it');
}
});
});
or even simpler;
$("#checkbox").attr("checked") ? alert("Checked") : alert("Unchecked");
If the checkbox is checked it will return true otherwise undefined

$(document).on('click','#checkBoxId',function(){
var isChecked = $(this).is(':checked');
console.log(isChecked);
});
This code above works also on bootstrap modal. isChecked is true or flase ;

Simple Demo for checking and setting a check box.
jsfiddle!
$('.attr-value-name').click(function() {
if($(this).parent().find('input[type="checkbox"]').is(':checked'))
{
$(this).parent().find('input[type="checkbox"]').prop('checked', false);
}
else
{
$(this).parent().find('input[type="checkbox"]').prop('checked', true);
}
});

Just to say in my example the situation was a dialog box that then verified the check box before closing dialog. None of above and How to check whether a checkbox is checked in jQuery? and jQuery if checkbox is checked did not appear to work either.
In the end
<input class="cb" id="rd" type="checkbox">
<input class="cb" id="fd" type="checkbox">
var fd=$('.cb#fd').is(':checked');
var rd= $('.cb#rd').is(':checked');
This worked so calling the class then the ID. rather than just the ID. It may be due to the nested DOM elements on this page causing the issue. The workaround was above.

For checkbox with an id
<input id="id_input_checkbox13" type="checkbox"></input>
you can simply do
$("#id_input_checkbox13").prop('checked')
you will get true or false as return value for above syntax. You can use it in if clause as normal boolean expression.

Actually, according to jsperf.com, The DOM operations are fastest, then $().prop() followed by $().is()!!
Here are the syntaxes :
var checkbox = $('#'+id);
/* OR var checkbox = $("input[name=checkbox1]"); whichever is best */
/* The DOM way - The fastest */
if(checkbox[0].checked == true)
alert('Checkbox is checked!!');
/* Using jQuery .prop() - The second fastest */
if(checkbox.prop('checked') == true)
alert('Checkbox is checked!!');
/* Using jQuery .is() - The slowest in the lot */
if(checkbox.is(':checked') == true)
alert('Checkbox is checked!!');
I personally prefer .prop(). Unlike .is(), It can also be used to set the value.

Something like this can help
togglecheckBoxs = function( objCheckBox ) {
var boolAllChecked = true;
if( false == objCheckBox.checked ) {
$('#checkAll').prop( 'checked',false );
} else {
$( 'input[id^="someIds_"]' ).each( function( chkboxIndex, chkbox ) {
if( false == chkbox.checked ) {
$('#checkAll').prop( 'checked',false );
boolAllChecked = false;
}
});
if( true == boolAllChecked ) {
$('#checkAll').prop( 'checked',true );
}
}
}

Try this...
$(function(){
$('body').on('click','.checkbox',function(e){
if($(this).is(':checked')){
console.log('Checked')
} else {
console.log('Unchecked')
}
})
})

Toggle checkbox checked
$("#checkall").click(function(){
$("input:checkbox").prop( 'checked',$(this).is(":checked") );
})

Using this code you can check at least one checkbox is selected or not in different checkbox groups or from multiple checkboxes.
Using this you can not require to remove IDs or dynamic IDs. This code work with the same IDs.
Reference Link
<label class="control-label col-sm-4">Check Box 2</label>
<input type="checkbox" name="checkbox2" id="checkbox21" value=ck1 /> ck1<br />
<input type="checkbox" name="checkbox2" id="checkbox22" value=ck2 /> ck2<br />
<label class="control-label col-sm-4">Check Box 3</label>
<input type="checkbox" name="checkbox3" id="checkbox31" value=ck3 /> ck3<br />
<input type="checkbox" name="checkbox3" id="checkbox32" value=ck4 /> ck4<br />
<script>
function checkFormData() {
if (!$('input[name=checkbox2]:checked').length > 0) {
document.getElementById("errMessage").innerHTML = "Check Box 2 can not be null";
return false;
}
if (!$('input[name=checkbox3]:checked').length > 0) {
document.getElementById("errMessage").innerHTML = "Check Box 3 can not be null";
return false;
}
alert("Success");
return true;
}
</script>

Since it's mid 2019 and jQuery sometimes takes a backseat to things like VueJS, React etc. Here's a pure vanilla Javascript onload listener option:
<script>
// Replace 'admincheckbox' both variable and ID with whatever suits.
window.onload = function() {
const admincheckbox = document.getElementById("admincheckbox");
admincheckbox.addEventListener('click', function() {
if(admincheckbox.checked){
alert('Checked');
} else {
alert('Unchecked');
}
});
}
</script>

Your question is not clear: you want to give "checkbox array id" at input and get true/false at output - in this way you will not know which checkbox was checked (as your function name suggest). So below there is my proposition of body of your isCheckedById which on input take checkbox id and on output return true/false (it's very simple but your ID should not be keyword),
this[id].checked
function isCheckedById(id) {
return this[id].checked;
}
// TEST
function check() {
console.clear()
console.log('1',isCheckedById("myCheckbox1"));
console.log('2',isCheckedById("myCheckbox2"));
console.log('3',isCheckedById("myCheckbox3"));
}
<label><input id="myCheckbox1" type="checkbox">check 1</label>
<label><input id="myCheckbox2" type="checkbox">check 2</label>
<label><input id="myCheckbox3" type="checkbox">check 3</label>
<!-- label around inputs makes text clickable -->
<br>
<button onclick="check()">show checked</button>

You can try either any of the ways preferred, as in jQuery or JavaScript.
Get the value as below and assign to the variable then you if-else statements as per your requirement.
var getVal=$('#checkbox_id').is(":checked"); // jQuery
var getVal=document.getElementById("checkbox_id").checked //JavaScript
if (getVal==true) {
// perform task
} else {
// perform task
}

use code below
<script>
$(document).ready(function () {
$("[id$='chkSendMail']").attr("onchange", "ShowMailSection()");
}
function ShowMailSection() {
if ($("[id$='chkSendMail'][type='checkbox']:checked").length >0){
$("[id$='SecEmail']").removeClass("Hide");
}
</script>

Better method of retrieving values of checked input boxes via jQuery?

I have several checkboxes and a fake submit button to make an AJAX request:
<form>
<input type="checkbox" value="1"/>
<input type="checkbox" value="2" checked="checked"/>
<input type="checkbox" value="3"/>
<input type="checkbox" value="4" checked="checked"/>
<input type="button" onclick="return mmSubmit();"/>
</form>
Within the mmSubmit() method, I would like to retrieve an array of values that have been selected. Here is what I am currently doing.
mmSubmit = function() {
var ids = [];
$('input[type=checkbox]:checked');.each(function(index) {
ids.push($(this).attr('value'));
});
// ids now equals [ 2 , 4 ] based upon the checkbox values in the HTML above
return false;
};
I'm wondering if there is a shorthand method in jQuery used to retrieve the values into an array, or if what I have is already optimal.

I think this can be accomplished with map. Try the following..
mmSubmit = function() {
var ids = $('input[type=checkbox]:checked').map(function(){
return $(this).val();
}).get();
// ids now equals [ 2 , 4 ] based upon the checkbox values in the HTML above
return false;
};
Take a look at: jQuery Traversing/Map

Well you can use .val() instead of .attr('value').
$.serializeArray() may also do what you want (http://docs.jquery.com/Ajax/serializeArray).

It's needs some optimization, buts generally it is right way. My variant:
mmSubmit = function () {
var ids = [];
$('input[type=checkbox]').each(function () {
if (this.checked) {
ids[ids.length] = this.value;
}
});
return ids;
};
It's little faster.