Javascript get element index position in DOM array by class or id

Try like this

var matches = document.querySelectorAll("#asd");

If you want to search by class

var matches = document.querySelectorAll(".asd");

If you want an index of your code

try like this

var domElements = document.body.getElementsByTagName('*');

for(var i=0;i<domElements.length;i++){
   if(domElements[i].id==="asd"){
      // search by id 
      // index i 
   }
   if(domElements[i].className==="asd"){
      // search by class 
      // index i 
   }
}

Edit

There another way you can find index

try like this

var domElements = document.body.getElementsByTagName('*');
var domList= Array.prototype.slice.call(document.body.getElementsByTagName('*'));
var itemList = Array.prototype.slice.call(document.querySelectorAll(".asd"));
console.log(domList.indexOf(itemList[0])) // if you wanna find one index

//if you wanna search all index of class 

for(var i=0;i<itemList.length;i++)
  console.log(domList.indexOf(itemList[i]))

Not literal code but if you iterate over the dom elements

for (var i = 0; i < parentElement.children.length; i++) {
    var item = parentElement.children[i];
    if (item.getAttribute('id') === 'asd') {
        return i;
    }
}

This has the assumption that instead of selecting ALL DOM elements, you simply select the parentElement of your list of elements - this approach is more logical and certainly a lot more efficient.

I think you are asking this:

var li = document.querySelectorAll("li");
function cutlistitem(lielm) {
lielm.addEventListener("click", function () {
    lielm.classList.toggle("done")
})
};
li.forEach(cutlistitem);

I was creating a todo list app in which I created an unordered list of tasks to be done, in that <ul> every task was in an <li>. Now what I wanted is: to add an event listener to every li element for which I needed to grab every element of li list. I ran a forEach loop on every element of li list and added an event listener to each of the element. To get and index of the element you can use indexOf method.