how to add a data attribute to an element via javascript code example

Example 1: js get data attribute

var element = document.querySelector('.element');
var dataAttribute = element.getAttribute('data-name');
// replace "data-name" with your data attribute name

console.log(dataAttribute);

Example 2: html javascript find data attribute

//javascript get html data attribute
<button data-id="1" >Click</button>
<button data-id="2" >Click</button>
<button data-id="3" >Click</button>
const btns=document.querySelectorAll('button[data-id]');
[...btns].forEach(btn => console.log(btn.getAttribute('data-id')))