计算班级在特定事件发生之前出现了多少次

Question

In my code, when you click on one of the numbered Divs, it will alert the name of the class attached to the div. What I'm unsure of is how can I detect the number of previous occurrences of that class, so that, for example, if I clicked 2 it will alert myClass(1) to say it's the second occurrence of it? (assuming 0 would be the first?)

In need of plain vanilla Javascript for this one.

 function counter(itemClicked) { var theClass = itemClicked.className; alert(theClass); } 

 <div class="myClass" onclick="counter(this)">1</div> <div class="myClass" onclick="counter(this)">2</div> <div class="myClass" onclick="counter(this)">3</div> 

Answer 1

As written by Ryan, this is a highly insecure scenario which will break should the element have multiple classes (and possibly for other things too), however, for your example a simple indexOf will work:

 function counter(el) { let index = Array.from(document.getElementsByClassName(el.className)).indexOf(el); alert(++index); } 

 <div class="myClass" onclick="counter(this)">1</div> <div class="myClass" onclick="counter(this)">2</div> <div class="myClass" onclick="counter(this)">3</div>