I can only access the first element in h1. I also can create a button and click loop through h1 elements and switch on or off .textDecoration class. But my aim is to click which element I want step by one and switch on or off .textDecoration class.
var x = document.getElementsByTagName("h1")[0];
function myFunction() {
x.classList.toggle("textDecoration");
}
x.addEventListener("click", myFunction);.textDecoration {
text-decoration: line-through;
}<h1>Text-Decoration: line-through</h1>
<h1>Text-Decoration: line-through</h1>
<h1>Text-Decoration: line-through</h1>
<h1>Text-Decoration: line-through</h1>I suggest you delegate
document.getElementById("container").addEventListener("click", function(e) {
const tgt = e.target.closest("h1");
if (tgt) tgt.classList.toggle("textDecoration");
}).textDecoration {
text-decoration: line-through;
}<div id="container">
<h1>Text-Decoration: line-through</h1>
<h1>Text-Decoration: line-through</h1>
<h1>Text-Decoration: line-through</h1>
<h1>Text-Decoration: line-through</h1>
</div>Your question seems to me very poorly formulated, are you looking for that?
document.querySelectorAll('h1').forEach( (Hn,_,All_h1) =>
{
Hn.onclick =_=>
{
if (Hn.classList.toggle('textDecoration'))
All_h1.forEach( Hx=> Hx.classList.toggle('textDecoration', Hn===Hx) )
}
}).textDecoration {
text-decoration: line-through;
}<h1>Text-Decoration: line-through</h1>
<h1>Text-Decoration: line-through</h1>
<h1>Text-Decoration: line-through</h1>
<h1>Text-Decoration: line-through</h1>