Why void is better for iifes.

concat-with-void.js

// This is our first js file.  We haven't put a trailing ; on the end

var a = 3

alert(a)

// this is our second file, which we've concated on to the end of the first file to HTTP requests
void function(){
  
  alert('hi')
}()
  

// because ASI doesn't think that `void` means you want to continue your expression, this works

concated-with-bracket.js

// This is our first js file.  We haven't put a trailing ; on the end

var a = 3

alert(a)

// this is our second file, which we've concated on to the end of the first file to HTTP requests
(function(){
  
  alert('hi')
})()
  

// because ASI doesn't insert in a ; when it thinks you want to continue your expression, it tries to *execute the return from alert*
// and pass in the function in our second file.  D'oh.