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js vs jQuery addclass

HTML

<div>
  <h1 class="goodbye">
  Hello1
  </h1> 
  <h2 class="goodbye">
  Hello2
  </h2> 
  <h3 class="goodbye">
  Hello3
  </h3> 
</div>

CSS

.selected{
  color:red;
}

.goodbye{
  text-decoration:underline;
}

JavaScript

$(".goodbye").addClass( "selected" );
/*
var d = document.getElementsByClassName("goodbye");
console.log(d);
for(var i=0;i<d.length;i++){
d[i].className += " selected";
}
*/