Unable to retrieve type of HTML element using JavaScript

Question

I wanted to know how can we retrieve the type of the element with the tag name I am creating a code on a HTML form. There are all types of HTML input elements (textfield, button, datepicker).

What I want is that if the user selects a option from a drop down, disable the checkboxes. But the checkbox are generated using PHP loop and I have also passed id in the checkbox name, so I cannot use:

document.getElementsByName('checkbox');

The name of my checkbox is "checkbox", so i tried using:

document.getElementsByTagName('input');

which i for disabling the checkbox but this disabled all the input element on the page. Is there any solution for this? How I could use the type attribute with it as checkbox and disable on checkbox:

function  disabler()
{  
     checkboxes = document.getElementsByTagName('input');
     if(checkboxes.type='checkbox')
     {
        for(var i=1, n=checkboxes.length;i<n;i++)
        {
            checkboxes[i].disabled = true;//here i want to disable only the checkbox on page 
        }
 }
}

Please take the time to format your code readably when asking for help. — T.J. Crowder
– T.J. Crowder, Commented Oct 26, 2013 at 11:54

matewka · Accepted Answer · 2013-10-26 12:10:53Z

3

You're using assignment operator = NOT comparison ==. Replace this line

if(checkboxes.type='checkbox')

with

if(checkboxes.type == 'checkbox')

or a strict comparison operator === (compares also variable type, e.g. "0" === 0 is false but "0" == 0 is true)

if(checkboxes.type === 'checkbox')

Also you're trying to access type attribute of a collection returned by getElementsByTagName. To access specific element refer to checkboxes as it was an array

if(checkboxes[0].type === 'checkbox') //accesses first checkbox element

To loop through all elements while checking each one if it is a checkbox do this

for(var i=0; i < checkboxes.length; i++)
    {
        if(checkboxes[i].type === 'checkbox') {
            checkboxes[i].disabled = true;
        }
    }

Here's an example fiddle for you

edited Oct 26, 2013 at 12:10

answered Oct 26, 2013 at 11:53

matewka

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5 Comments

nnnnnn Over a year ago

You're right that = is the wrong operator, but testing checkboxes.type is also wrong in that checkboxes is a list...

Meenesh Jain Over a year ago

ya i tried if(checkboxes.type === 'checkbox') but it didnt worked...!

matewka Over a year ago

@MeeneshJain, I edited the answer. See the last line of code.

Meenesh Jain Over a year ago

sir i used === it makes my code non working ..... only = works fine but it disables all input on that page

matewka Over a year ago

Sorry, I had to update it again. Please check it now. Use the last block of code (6 lines).

T.J. Crowder · Accepted Answer · 2013-10-26 11:53:18Z

2

In JavaScript, = is an assignment operator. == and === are the equality operators (loose and strict, respectively). So:

if(checkboxes.type=='checkbox')  // Loose, does type conversion (not relevant here)

or

if(checkboxes.type==='checkbox') // Strict, no type conversion (not relevant here)

answered Oct 26, 2013 at 11:53

T.J. Crowder

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Comments

Barmar · Accepted Answer · 2013-10-26 11:55:03Z

2

checkboxes is a Node List, not a single element. You need to do the test on checkboxes[i]:

function  disabler()
{  
    checkboxes = document.getElementsByTagName('input');
        for(var i=1, n=checkboxes.length;i<n;i++)
        {
            if (checkboxes[i].type == 'checkbox') {
                checkboxes[i].disabled = true;
            }
        }
}

answered Oct 26, 2013 at 11:55

Barmar

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