Writing great Javascript | Hacker News Reader

Writing great Javascript

oli.me.uk

76 pointsneya10 comments

I've never seen the preceding semi-colon like that. It makes perfect sense, there are a lot of JavaScript coders these days coming from languages like Ruby and these people often don't use semi-colons, very smart advice to protect against that!

The preceding semi-colon is definitely a very smart advice. I also will have to try out jshint (I've been using jslint).

Adding a leading semicolon just in case seems like overly defensive programming to me. You ought to pick trustworthy tools. If your script concatenator doesn't work right, I think it's better to fail fast rather than let things quietly be half-broken all over the place.

You ought to pick trustworthy tools.

Many JavaScript snippets are made to be integrated and added by other people on their websites.

It doesn't even need to be a semicolon. It's also common to see a ! used for this purpose.

You really only need one or the other depending on the style of the code you are using in the rest of your project.

If you write js using semi-colons everywhere:

    (function () { })(this);

    (function () { })(this);

    (function () { })(this);

If you dont want to use semi-colons unless you have to:

    ;(function () { })(this)

    ;(function () { })(this)

    ;(function () { })(this)

Basically, never start lines with `(` or `[` without semis and don't throw in line breaks liberally without understanding what semicolon insertion is going to happen.

http://blog.izs.me/post/2353458699/an-open-letter-to-javascr...

But what if you do this:

    <script src='3rdpartyA.js'></script>
    <script src='yourscript.js'></script>
    <script src='3rdpartyB.js'></script>

You need the semicolon at both ends to insulate your script from the unknown coding style or 3rd party scripts which may be appended or prepended to yours.

If 3rd party A omits a trailing semicolon, or 3rd party B doesn't uses your semicolon prefix style then by wrapping your script in semicolons you pre-emptively prevent problems.

I believe this is an example of the wider coding style called "defensive coding".

Or you could actually just read the source code of the libs you are using...

It's pretty easy to miss a terminating semicolon which will waste time, but the real use case is for people who are writing the libs that other people are using; they have absolutely no knowledge or control of what other javascript might be prependend or appended onto theirs.

Yeah. So I add a trailing semicolon. Then the 3rd party library releases an update. I have to remember to merge my patch every time they update, do I?

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