How to check if a checkbox is checked in javascript?

Question

I have multiple checkboxes and I would like to know if one of them is checked. My code does not give me any error, but I don't get the results I am expecting. When I run the code always get the first alert which is inside the for loop. The following is my code:

function validate(){


    if(document.getElementById('postTW').checked || document.getElementById('postFB') ){

        var checker = document.getElementsByName('twitter[]');
        for (var i = 0; i < checker.length; i++) {
            if(checker[i].checked){
                return true;
            }

            else{

                alert("Not enough arguments ");

                return false;
            }
        };

    }


    else{
        alert("Not enough arguments to submit the form");

        return false;
    }

}

My form is method = post and looks like the following

<input class="twGroup" type="checkbox" name="twitter[]" value="x"/> 
<input class="twGroup" type="checkbox" name="twitter[]" value="y"/>
<input class="twGroup" type="checkbox" name="twitter[]" value="z"/>

@Arjuna I just edited my question, you can see part of the form now — Alexander
– Alexander, Commented Jul 15, 2014 at 6:44
@Bart How can I iterate through all the checkboxs, thanx in advanced — Alexander
– Alexander, Commented Jul 15, 2014 at 6:45

Andrei 'finelord' Baibakou · Accepted Answer · 2014-07-15 06:46:19Z

2

This code checks only 1st checkbox because of return:

for (var i = 0; i < checker.length; i++) {
    if(checker[i].checked) {
        return true;
    } 
    else {
        alert("Not enough arguments ");
        return false;
    }
};

Try this:

var checked_flag = false;
for (var i = 0; i < checker.length; i++) {
    if(checker[i].checked) {
        checked_flag = true;
    }         
};
return checked_flag;

answered Jul 15, 2014 at 6:46

Andrei 'finelord' Baibakou

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Comments

Carson Ip · Accepted Answer · 2014-07-15 06:48:38Z

2

Are there logic errors in the following code?

for (var i = 0; i < checker.length; i++) {
        if(checker[i].checked){
            return true;
        }

        else{

            alert("Not enough arguments ");

            return false;
        }
    };

I assume you want something like this:

var flag=false;
for (var i = 0; i < checker.length; i++) {
            if(checker[i].checked){
                flag=true;
            }
        };
if (!flag){
        alert("Not enough arguments ");
}

answered Jul 15, 2014 at 6:48

Carson Ip

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1 Comment

Alexander Over a year ago

yeah, I followed a different approach but I am sure this woks as well. Thank you

nraina · Accepted Answer · 2014-07-15 07:01:36Z

2

Use a flag that will return false if any checkbox of name twitter[] is not checked

function validate(){
 if(document.getElementById('postTW').checked || document.getElementById('postFB').checked ){
   var result = true;
    var checker = document.getElementsByName('twitter[]');
    for (var i = 0; i < checker.length; i++) {
        if(!checker[i].checked){
            alert("Not enough arguments ");
            result = false;
            return;
        }
    };
}
else{
    alert("Not enough arguments to submit the form");
    result = false;
}
return result

}

answered Jul 15, 2014 at 7:01

nraina

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1 Comment

Alexander Over a year ago

I think your approach is right, but i solve my problem already. Thank you very much though

muj · Accepted Answer · 2014-07-15 06:48:58Z

1

Looks like you have a logical error in your code. As written, if the first checkbox is not checked, then you will fall through to the else statement and display the alert. You should simply get rid of the first else statement and move the first alert outside of the for-loop:

function validate() {
    if(document.getElementById('postTW').checked || document.getElementById('postFB') ) {
        var checker = document.getElementsByName('twitter[]');
        for (var i = 0; i < checker.length; i++) {
            if(checker[i].checked){
                return true;
            }
        };

        // else fall through
        alert("Not enough arguments ");
        return false;
    }
    else {
        alert("Not enough arguments to submit the form");
        return false;
    }
}

answered Jul 15, 2014 at 6:48

muj

1637 bronze badges

1 Comment

Alexander Over a year ago

Actually it works, I forgot to get rid of the else part. Thank you

JayKandari · Accepted Answer · 2014-07-15 06:56:03Z

1

wrap your checkboxes around <form> element. Example shown:

<form name="myform">
    <input type="checkbox" name="twitter[]" />
    <input type="checkbox" name="twitter[]" checked="checked" />
    <input type="checkbox" name="twitter[]" />
    <input type="checkbox" name="twitter[]" checked="checked" />
    <input type="checkbox" name="twitter[]" />
</form>

Apply Javascript as shown.

    if (document.getElementById('postTW').checked || document.getElementById('postFB')) {
        var myform = document.forms.myform;
        var elems = myform.elements['twitter[]'];
        for (var i = 0; i < elems.length; i++) {
            if (elems[i].checked) {
                return true;
            }
        }
        alert("Not enough arguments to submit the form");
        return false;

    } else {
        alert("Not enough arguments to submit the form");
        return false;
    }

answered Jul 15, 2014 at 6:56

JayKandari

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2 Comments

Alexander Over a year ago

Thank you, somebody else suggested your solution and it works perfectly

Alexander Over a year ago

you are fine, at least you knew the answer which is always good

user63762453 · Accepted Answer · 2014-07-15 06:53:02Z

0

Don't you think you should write:

if(document.getElementById('postTW').checked || document.getElementById('postFB').checked ){

instead of:

if(document.getElementById('postTW').checked || document.getElementById('postFB') ){

edited Jul 15, 2014 at 6:53

answered Jul 15, 2014 at 6:41

user63762453

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