Can't update data-attribute value

Although there are some examples of this on the web, it does not seem to work correctly. I can't figure out the problem.

I have this simple HTML

<div id="foo" data-num="0"></ div>
<a href="#" id="changeData">change data value</a>

Every time I click the link "change data value" I want to update the data value of data-num. For example, I need it to be 1,2,3,4,... (plus 1 every time I click the link)

what I have is

var num = $('#foo').data("num");
console.log(num);
num = num+1;               
console.log(num);
$('#foo').attr('data-num', num);   

The value changes one time from 0 to 1 every time. I can't make it incremental. Any suggestions on what I'm doing wrong?

Use that instead, if you wish to change the attribute data-num of node element, not of data object:

DEMO

$('#changeData').click(function (e) { 
    e.preventDefault();
    var num = +$('#foo').attr("data-num");
    console.log(num);
    num = num + 1;
    console.log(num);
    $('#foo').attr('data-num', num);
});

PS: but you should use the data() object in virtually all cases, but not all...

THE ANSWER BELOW IS THE GOOD ONE

You aren't using the data method correctly. The correct code to update data is:

$('#foo').data('num', num); 

So your example would be:

var num = $('#foo').data("num") + 1;       
console.log(num)       
$('#foo').data('num', num); 
console.log(num)

If we wanted to retrieve or update these attributes using existing, native JavaScript, then we can do so using the getAttribute and setAttribute methods as shown below:

JavaScript

<script>
// 'Getting' data-attributes using getAttribute
var plant = document.getElementById('strawberry-plant');
var fruitCount = plant.getAttribute('data-fruit'); // fruitCount = '12'

// 'Setting' data-attributes using setAttribute
plant.setAttribute('data-fruit','7'); // Pesky birds
</script>

Through jQuery

// Fetching data
var fruitCount = $(this).data('fruit');

// Above does not work in firefox. So use below to get attribute value.
var fruitCount = $(this).attr('data-fruit');

// Assigning data
$(this).data('fruit','7');

// But when you get the value again, it will return old value. 
// You have to set it as below to update value. Then you will get updated value.
$(this).attr('data-fruit','7'); 

Read this documentation for vanilla js or this documentation for jquery

For myself, using Jquery lib 2.1.1 the following did NOT work the way I expected:

Set element data attribute value:

$('.my-class').data('num', 'myValue');
console.log($('#myElem').data('num'));// as expected = 'myValue'

BUT the element itself remains without the attribute:

<div class="my-class"></div>

I needed the DOM updated so I could later do $('.my-class[data-num="myValue"]') //current length is 0

So I had to do

$('.my-class').attr('data-num', 'myValue');

To get the DOM to update:

<div class="my-class" data-num="myValue"></div>

Whether the attribute exists or not $.attr will overwrite.

Had similar problem and in the end I had to set both

obj.attr('data-myvar','myval')

and

obj.data('myvar','myval')

And after this

obj.data('myvar') == obj.attr('data-myvar')

Hope this helps.

Basically, there are two ways to set / update data attribute value, depends on your need. The difference is just, where the data saved,

If you use .data() it will be saved in local variable called data_user, and its not visible upon element inspection, If you use .attr() it will be publicly visible.

Much clearer explanation on this comment

This answer is for those seeking to just change the value of a data-attribute

The suggested will not change the value of your Jquery data-attr correctly as @adeneo has stated. For some reason though, I'm not seeing him (or any others) post the correct method for those seeking to update their data-attr. The answer that @Lucas Willems has posted may be the answer to problem Brian Tompsett - 汤莱恩 is having, but it's not the answer to the inquiry that may be bringing other users here.

Quick answer in regards to original inquiry statement

-To update data-attr

$('#ElementId').attr('data-attributeTitle',newAttributeValue);

Easy mistakes* - there must be "data-" at the beginning of your attribute you're looking to change the value of.

Had a similar problem, I propose this solution althought is not supported in IE 10 and under.

Given

<div id='example' data-example-update='1'></div>

The Javascript standard defines a property called dataset to update data-example-update.

document.getElementById('example').dataset.exampleUpdate = 2;

Note: use camel case notation to access the correct data attribute.

Source: https://developer.mozilla.org/en-US/docs/Learn/HTML/Howto/Use_data_attributes

I had the same problem of the html data tag not updating when i was using jquery But changing the code that does the actual work from jquery to javascript worked.

Try using this when the button is clicked: (Note that the main code is Javascripts setAttribute() function.)

function increment(q) {

    //increment current num by adding with 1
    q = q+1;

    //change data attribute using JS setAttribute function
    div.setAttribute('data-num',q);

    //refresh data-num value (get data-num value again using JS getAttribute function)
    num = parseInt(div.getAttribute('data-num'));

    //show values
    console.log("(After Increment) Current Num: "+num);

}

//get variables, set as global vars
var div = document.getElementById('foo');
var num = parseInt(div.getAttribute('data-num'));

//increment values using click
$("#changeData").on('click',function(){

    //pass current data-num as parameter
    increment(num);

});