[javascript] How can I get the values of data attributes in JavaScript code?

I have next html:

<span data-typeId="123" data-type="topic" data-points="-1" data-important="true" 
    id="the-span"></span>

Is it possible to get the attributes that beginning with data-, and use it in the JavaScript code like code below? For now I get null as result.

document.getElementById("the-span").addEventListener("click", function(){
    var json = JSON.stringify({
        id: parseInt(this.typeId),
        subject: this.datatype,
        points: parseInt(this.points),
        user: "H. Pauwelyn"
    });
});

You could also grab the attributes with the getAttribute() method which will return the value of a specific HTML attribute.

var elem = document.getElementById('the-span');_x000D_
_x000D_
var typeId = elem.getAttribute('data-typeId');_x000D_
var type   = elem.getAttribute('data-type');_x000D_
var points = elem.getAttribute('data-points');_x000D_
var important = elem.getAttribute('data-important');_x000D_
_x000D_
console.log(`typeId: ${typeId} | type: ${type} | points: ${points} | important: ${important}`_x000D_
);

<span data-typeId="123" data-type="topic" data-points="-1" data-important="true" id="the-span"></span>

Modern browsers accepts HTML and SVG DOMnode.dataset

Using pure Javascript's DOM-node dataset property.

It is an old Javascript standard for HTML elements (since Chorme 8 and Firefox 6) but new for SVG (since year 2017 with Chorme 55.x and Firefox 51)... It is not a problem for SVG because in nowadays (2019) the version's usage share is dominated by modern browsers.

The values of dataset's key-values are pure strings, but a good practice is to adopt JSON string format for non-string datatypes, to parse it by JSON.parse().

Using the dataset property in any context

Code snippet to get and set key-value datasets at HTML and SVG contexts.

console.log("-- GET values --")_x000D_
var x = document.getElementById('html_example').dataset;_x000D_
console.log("s:", x.s );_x000D_
for (var i of JSON.parse(x.list)) console.log("list_i:",i)_x000D_
_x000D_
var y = document.getElementById('g1').dataset;_x000D_
console.log("s:", y.s );_x000D_
for (var i of JSON.parse(y.list)) console.log("list_i:",i)_x000D_
_x000D_
console.log("-- SET values --");_x000D_
y.s="BYE!"; y.list="null";_x000D_
console.log( document.getElementById('svg_example').innerHTML )

<p id="html_example" data-list="[1,2,3]" data-s="Hello123">Hello!</p>_x000D_
<svg id="svg_example">_x000D_
  <g id="g1" data-list="[4,5,6]" data-s="Hello456 SVG"></g>_x000D_
</svg>

You can access it as

element.dataset.points

etc. So in this case: this.dataset.points

Try this instead of your code:

var type=$("#the-span").attr("data-type");
alert(type);

Because the dataset property wasn't supported by Internet Explorer until version 11, you may want to use getAttribute() instead:

document.getElementById("the-span").addEventListener("click", function(){
  console.log(this.getAttribute('data-type'));
});

Dataset documentation

getAttribute documentation

Circa 2019, using jquery, this can be accessed using $('#DOMId').data('typeId') where $('#DOMId') is the jquery selector for your span element.

if you are targeting data attribute in Html element,

document.dataset will not work

you should use

document.querySelector("html").dataset.pbUserId

or

document.getElementsByTagName("html")[0].dataset.pbUserId