The getElementsByClassName method returns an HTML collection which containing all the elements with the specified class name. To add a class to the elements in the collection, you need to loop through the collection and add the class to each individual element.
Try this:
if (location.href.indexOf('url') > -1) {
var elements = document.getElementsByClassName('className');
for (var i = 0; i < elements.length; i++) {
elements[i].classList.add('NewClass');
}
}
In this code, we first store the HTML collection in the elements variable. Then, we iterate over each element in the collection using a for loop and add the class 'NewClass' to each individual element using the classList.add method.