Untitled

document.getElementsByClassName( "myclass" ).forEach( function(element, index, array) {
  //do stuff
});

[2, 5, 9].forEach( function(element, index, array) {
  //do stuff
});

var els = document.getElementsByClassName("myclass");
var elsArray = Array.prototype.slice.call(els, 0);
elsArray.forEach(function(el) {
    // Do stuff with the element
    console.log(el.tagName);
});

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <script>
            function findTheOddOnes()
            {
                var theOddOnes = document.getElementsByClassName("odd");
                for(var i=0; i<theOddOnes.length; i++)
                {
                    alert(theOddOnes[i].innerHTML);
                }
            }
        </script>
    </head>
    <body>
        <h1>getElementsByClassName Test</h1>
        <p class="odd">This is an odd para.</p>
        <p>This is an even para.</p>
        <p class="odd">This one is also odd.</p>
        <p>This one is not odd.</p>
        <form>
            <input type="button" value="Find the odd ones..." onclick="findTheOddOnes()">
        </form>
    </body>
</html>