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Why not support this valid JavaScript

Why not support this valid JavaScript?

Every once in a while I get asked why doesn't JSDuck support a certain character in the names of various entities. The character is usually some punctuation like the dot (.) or dash (-). The names in question are the names of classes and class members (methods, properties, events, etc).

So why doesn't JSDuck allow you to document a class named My.Special-Class or method named my+method? Why doesn't the freaking tool just get out of the way and allow you to do what you want? Supporting just one more character can't be so hard - why not simply do it?

Three reasons:

It's not sensible

The problem here is that JavaScript, unlike most other object-oriented languages, doesn't require the names of object properties and methods to be proper identifier names. Objects are just hash tables - any string is a valid key, and therefore also a valid method/property name.

So when I implement support for dash and dot, the next user comes along and asks why doesn't JSDuck support colon? Then the third one comes and asks to support spaces. Soon we're talking about supporting the whole Unicode including Egyptian hieroglyphs.

A tourist studying Egyptian hieroglyphs

We need to practice some moderation. Thankfully JavaScript itself gives us some guidance on this: although we can name methods with any imaginable string, like so:

window["My class"]["ho-ho-hoo!"]();

only when using proper identifier names will they be convenient to use:

MyClass.hoHoHoo();

So, by only allowing proper identifier names, JSDuck is asking you to take the sensible route.

The main thing here is that JSDuck is opinionated. It wants you to write your code in a certain way. And if you want to do things differently it's going to be painful. In that case you might have chosen the wrong tool.

It's troublesome to implement

In addition to the above, supporting the whole range of possible characters is far from easy to implement. Even adding support for just one more punctuation character is a considerable amount of work.

Hard working woman

There's a lot of convenience that derives from the assumption that class and member names are always proper identifier names. It allows us to use the same names in URL-s, HTML id-s and other generated code without a need to do additional escaping.

For example when supporting dot in member names, we need to ensure we encode the dot somehow when using the name inside HTML id attribute, because the following is not valid:

<p id="ho.ho.hoo">

JSDuck is already doing this kind of escaping to support the $ character which is valid in JavaScript identifiers but invalid as HTML id. So an identifier $foo becomes S-foo in HTML. Not a prettiest solution, but it's a mandatory thing for a JavaScript documentation tool to support.

But supporting all kinds of other characters is just complicating the code base while helping only a rary minority of users who want to do some weird things.

It's not just JSDuck

Finally, using non-identifier names for classes and members is just asking for trouble. Even if JSDuck implements a support for it, you will soon face some other tool which also chokes on your unconventional code. Sure, you can have a slash (/) in your class names, but good luck with your filesystem if you want to save it into a file with the same name.

German shepherd jumping through a ring of fire

But in the end there's nothing to stop you. Go ahead, write the craziest JavaScript possible. I do encourage you. It's the land of the wild and brave. But it's not the land of great tooling support.

Photo credits: Het Leven, 1927, Copying Egyptian hieroglyphs; Lewis W. Hine, 1920, Woman with Machine; George Jackman, Ten lords a' leaping.

Kirjutatud 17. septembril 2012.

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