javascript last index of is the same as indexof code example

Example 1: get all the child of the same class javascript

var doc = document.getElementById("test");
var notes = null;
for (var i = 0; i < doc.childNodes.length; i++) {
    if (doc.childNodes[i].className == "4") {
      notes = doc.childNodes[i];
      break;
    }        
}

Example 2: array index javascript show only first 2 elements

array.slice(0, n);