Make your code the best comment ever.
The undocumented array
Let's start with a simple line of JavaScript:
const a = [];
Well... that's an array declaration: no big deal. What will be this array used for?
Hard to say without any context, plus the variable name isn't helping. Here is the context: I'm working on a side project using React and React Router (v6). Here is the real code, with a real variable name, in a file named routes.js
:
const routes = [
{ path: '/foo', element: <Foo /> },
{ path: '/bar', element: <Bar /> }
];
export default routes;
Here you are: the array will list the routes of the application. Then you may use it:
import { useRoutes } from "react-router";
import routes from './routes';
export default function App() {
return useRoutes(routes);
}
Of course, I didn't invent that pattern. I saw a similar code, and wanted to make it a template repository on GitHub. Some kind of personal React framework. Thus the array should be empty in routes.js
. Indeed the template shouldn't declare any route: I don't know the application I will build from my framework.
const routes = [];
export default routes;
I will remember how it should be filled since that's my own code... at least a while.
Eagleson's law
You may have heard it:
"Any code of your own that you haven't looked at for six or more months might as well have been written by someone else."
Sure I would be thankful to myself 6 months later — or next week — if I add some comment:
/* route format: {path: '/foo', element: <Foo />} */
const routes = [];
export default routes;
It may looks ok at first glance, but looking closer it's not. Really not. First, I can't expect anyone — including me — to understand this comment. It describes something as a route format. It doesn't explain what to do with the routes
array. In fact it's only useful if you already know what to do. Good enough for a reminder, but not what you would expect of a documentation.
And there is an other issue. Do you always read comments in code? I don't. Hours of code reading trained my eyes and my brain to ignore them as much as they can. I'm used to see comments as pollution between 2 lines of code.
Let's see the glass half full. Now we have a checklist to write useful documentation:
- you should express it in a explicit, non-ambiguous form,
- you should ensure it will be read.
"Explicit, non-ambiguous expression" doesn't look like a definition of writing, but of coding. You can't be sure any human will read what you wrote. But would you ask a program, you can always be sure it will "read" your code. So why not coding the documentation? A code version of this comment:
/* route format: {path: '/foo', element: <Foo />} */
When the best comment is the code itself
That's where TypeScript can help us. In a nutshell, you can use TypeScript to describe the type of value expected for a variable:
const anyValue = '42'; // standard JS: will never complain
const anyString: string = '42'; // ok: '42' is a string
const anyNumber: number = '42'; // no: '42' is not a number
That's for primitives. Would you need to ensure an object has specific, typed properties you can define an interface or a type alias:
interface MyInterface {
anyString: string;
anyNumber: number;
}
const myObject: MyInterface = {
anyString: '42',
anyNumber: '42', // again, wrong type !!!
};
And that's what we need. Instead of a not-sure-to-be-useful comment, we can "type" the array. This will describe its future content:
import { ReactNode } from "react";
interface MyRoute {
path: string;
element: ReactNode;
}
const routes: MyRoute[] = [];
export default routes;
TypeScript can't misunderstand this, and it will never forget to read it. You can try it with an invalid object:
import { ReactNode } from "react";
interface MyRoute {
path: string;
element: ReactNode;
}
const routes: MyRoute[] = [
{ whenToRender: '/foo', whatToRender: <Foo /> }
];
export default routes;
This will output something like that:
Type '{ whenToRender: string; whatToRender: any; }' is not assignable to type 'MyRoute'
Object literal may only specify known properties, and 'whenToRender' does not exist in type 'MyRoute'
That's how TypeScript can help you to self-document your code ;)
Top comments (1)
Nice