Rails offers a variety of methods for generating unique DOM IDs and classes for elements on a page. One such method is the dom_id method, which can generate a unique ID for a specific object or model. However, by default, the dom_id method only generates an ID and does not include any classes.

Recently, however, Rails has added a new feature that allows the dom_id method to also accept a class. This allows developers to generate both an ID and a class for an element without the need to use different methods for generating IDs and classes.

Before

Before this feature was added, developers would have to use the dom_id method to generate an ID, and then use a separate method such as dom_class to generate a class.

Here, developers would have to use separate methods to generate both an ID and a class for an element. Let’s assume we have a User model and we want to generate the dom_id and dom_class for it. We would write the following code:

<div id="<%= dom_id(@user) %>" class="<%= dom_class(@user) %>">
  <!-- user related content -->
</div>

As we can see, this requires two separate lines of code, one for the ID and one for the class.

After

With the new feature, developers can now generate both an ID and a class in a single line of code using the dom_id method. For example:

<div <%= dom_id(@user, :class) %>>
  <!-- user related content -->
</div>

As we can see, this is a much more concise and efficient way of generating both an ID and a class.

Additionally, if we want to add a custom class, we can pass it as a second parameter.

<div <%= dom_id(@user, class: "custom-class") %>>
  <!-- user related content -->
</div>

Now, they can use the dom_id method to generate both an ID and a class at the same time, saving them a few keystrokes.

Overall, the ability for the dom_id method to accept a class in Rails is a welcome addition for developers. With this PR, developers can write more efficient and maintainable code.