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.

See also: https://stackoverflow.com/questions/1873983/what-does-the-le...

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.