You Don't Need Trailing Semicolons

I was discussing semicolons with a coworker recently, when I (rather inelegantly) made a case for omitting semicolons from a new JavaScript project. I'm rephrasing it here because I don't often see this perspective in the endless public debate about semicolons in JS.

The JavaScript community has a history of piling on those who advocate semicolon-free code (although the tide does seem to be turning of late). For a long time, I was in the pro-; camp. While semicolon-free code has always looked easier to read and “cleaner” to my eyes, why would you seemingly invite bugs into your software for such a small aesthetic benefit? Also, Douglas Crockford forbade them (his views are apparently still a primary factor in the style choices of many JavaScript developers).

Before getting into the crux of my argument, I must concede that if you write your JavaScript without trailing semicolons, you need to make a habit of adding them to the start of the line in two specific cases – when you begin your line with a [ or a (. Otherwise in some cases JavaScript will interpret those characters as the start of array indexing or function invocation, respectively.

Anyways, I was experimenting with semicolon-free JS on a side project a few months ago when I tripped up and forgot the two edge cases above. What I saw caused me to swear off trailing semicolons for all future projects. It looked something like this:

Semicolon enlightenment

The screenshot above shows JSHint catching the two aforementioned cases where omitting trailing semicolons could cause a bug in JavaScript. The beauty in this example is that this feedback happened instantly in my editor (via syntastic in Neovim).

If you don't have a linter making these (and other) automated checks for you before you check in, a) you're missing out, and b) please refrain from lecturing others on programming style and code quality. If you do have linting checks in place, you can skip trailing semicolons. It's up to you, but with today's tooling support for JavaScript, code "quality" and robustness should not factor into your decision.

Further / reading / on / semicolons. Also, for a good time, read this entire thread

Postscript: There are a few more contrived cases where ASI can bite you, but in my experience they're not worth worrying about:

function thisIsTerrible() {
    return              // ASI would strike here; returns `undefined`
        foo: 'bar'

Seriously, who writes code like this? Oh yeah, and JSHint will catch this too.