Evan X. Merz

musician/technologist/human being

Single File Components are Good

I was reading the Vue.js documentation recently, and I came across a very compelling little passage. The passage was explaining the thinking behind single file components. In a single file component, the template, javascript logic, and perhaps even styles, are all collocated in the same file.

Putting all the parts of a component into a single file may seem odd to some programmers. After all, shouldn’t we be separating logic from templates? Shouldn’t we be separating styles from logic too?

And the answer is that the right thing to do is situation dependent, and this is something that a lot of modern programmers don’t understand. A lot of programmers seem to think that there are rules, and you must follow the rules. They don’t realize that rules should only be followed when they are helping you.

So the core question is this: is separating a single view into several files really helping your development process?

Here’s what the Vue documentation says.

One important thing to note is that separation of concerns is not equal to separation of file types. In modern UI development, we have found that instead of dividing the codebase into three huge layers that interweave with one another, it makes much more sense to divide them into loosely-coupled components and compose them. Inside a component, its template, logic and styles are inherently coupled, and collocating them actually makes the component more cohesive and maintainable.

So the argument from the Vue developers is that keeping all the code related to one view inside one file is actually more maintainable than separating them.

I tentatively agree with this.

Obviously, it’s good to separate certain things out into their own files. Foundational CSS styles and core JS helper methods should have their own place. But for all the code that makes a component unique, I think it’s easiest for developers if that is in one file.

Here are the problems I face with breaking a view into multiple files.

1. What is each file called? Where is it located?

When you separate a view into multiple files, it becomes difficult to find each file. It’s fine to have a standard for naming and locating files, but in any large software project, there are going to be situations where the standard can’t be followed for one reason or another. Maybe the view was created early in development. Maybe the view is shared. Or maybe the view was created by a trainee developer and the mis-naming was missed in the code review. Whatever the cause, file names and locations can be stumbling blocks.

At my workplace, we have hundreds of templates named item.js.hamlbars. That’s not very helpful, but what’s more troublesome is when, for whatever reason, a list item couldn’t be named item.js.hamlbars. In that case, I’m left searching for files with whatever code words I can guess.

2. Where is the bug?

When you separate a view into multiple files, you don’t know where a bug may be coming from. This is especially troublesome if you are in a situation where conditional logic is being put into the templates. Once you have conditional logic in the templates, then you can’t know if the bug is in the javascript or in the template itself. Furthermore, it then takes developer time to figure out where to put the fix.

Single File Components are a Bonus

Putting all the code for a single view into a single file is not only logical, but it also doesn’t violate the separation-of-concerns ethos. While the pieces are all in the same file, they each have a distinct section. So this isn’t the bad old days of web development, where javascript was strewn across a page in any old place. Rather, collocating all the code files for a single view is a way to take away some common development headaches.

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Evan X. Merz

Evan X. Merz holds degrees in computer science and music from The University of Rochester, Northern Illinois University, and University of California at Santa Cruz. He is a programmer, musician, and author of Empress blog software. He makes his online home at evanxmerz.com.