getElementsByClassNameclassNames

The `getElementsByClassName` method is a fundamental JavaScript function used to retrieve a collection of elements from an HTML document that have a specific class name. It is a part of the Document Object Model (DOM) API. When you call `getElementsByClassName` on an element or the document itself, you provide a string containing one or more class names. The method then searches the document or the specified element's descendants for all elements that possess all of the specified class names.

The result of `getElementsByClassName` is an HTMLCollection, which is a live, array-like object. "Live" means that if elements are added or removed from the DOM that match the criteria, the HTMLCollection will automatically update to reflect these changes. While it's array-like, it's not a true JavaScript array, meaning it doesn't have all array methods like `map` or `filter` directly available. However, you can iterate over an HTMLCollection using a standard for loop or convert it to an array using `Array.from()` or the spread syntax (`[...]`).

The `classNames` argument to `getElementsByClassName` can be a single class name or a space-separated string of multiple class names. If multiple class names are provided, an element must have all of them to be included in the returned collection. For example, `document.getElementsByClassName('foo bar')` will return elements that have both the 'foo' and 'bar' classes. This method is a powerful tool for DOM manipulation, allowing developers to easily select and work with groups of elements based on their class assignments.