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Comment by recursive | Hacker News Reader

Can anyone explain why there's a leading semi-colon in the inline script example? AFAICT it doesn't do anything.

Some people for some reason write javascript without semicolons, if they do that you cant safely concatenate javascript files together since the file2 may modify file1's last expression, putting a ; at the start guarantees to complete the last files expression if they havent already done so. A bunch of concatenators will do this automatically / by default

You are correct that this is an issue when writing JavaScript without semicolons, but it's also an issue if you place an IIFE (immediately invoked function expression) directly after a function, even if you're using semicolons:

  function hasSemicolons() {
    console.log('hello world');
  }

  (function() {
    console.log('this is broken, JS will call hasSemicolons()');
  })()

In the ImmortalDB example, since it's a standalone <script> tag this is just extra defensive against a minifier that would join the tag with other tags, but just wanted to call out that there's a reason to include the leading semicolon in front of an IIFE whether or not you write your JavaScript with semicolons.

Your snippet doesn't fail. This one does

    console.log('this doesn't work!')
    (false ? console.log : console.error)('this will fail with a TypeError')
    >> Uncaught TypeError: console.log(...) is not a function

    console.log('this works!')
    ;(true ? console.log : console.error)('hello world')

So I tested this out in Firefox. I think you're wrong. I never see 'hello world' even if I remove all the whitespace between the functions.

There is a reason why that issue with IIFEs can be hit, and it's because you've omitted some semicolons - granted they are the sort that most people omit.

Since everything in js is a statement the correct semi-colon syntax for the above is

  function hasSemicolons() {
    console.log('hello world');
  };

  (function() {
    console.log('this is broken, JS will call hasSemicolons()');
  })();

The ECMAScript specification (https://www.ecma-international.org/publications/files/ECMA-S...) has statements in a separate chapter from function declarations. (Chapter 14) Furthermore, the function declaration grammar does not contain a semi-colon, unlike other statements.

When you're dealing with JS files it makes sense, but the example is an inline <script> tag. It might be an abundance of caution just in case you're dealing with CDN optimizers that slice and dice inline scripts. I've experienced that with Akamai a few times.

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