What makes Go's semicolon insertion algorithm different from JavaScript's? They ...

xigoi · on July 7, 2024

The following (contrived) JavaScript code does not work:

  let x = 5
  (function() { console.log(x) })()

The equivalent Go code works:

  package main
  import "fmt"
  func main() {
    x := 5
    (func() { fmt.Printf("%d", x) })()
  }

trealira · on July 7, 2024

Thanks, that's a good case.

Actually, the JavaScript semicolon insertion algorithm [0] seems more complex than I had remembered. I had thought of them as variations on the semicolon insertion in BCPL, but it seems like that's an oversimplification.

For reference, these are the BCPL rules:

The canonical symbol SEMICOLON is inserted between pairs of items if they appeared on different lines and if the first was from the set of items which may end a command or definition, namely:

  BREAK RETURN FINISH REPEAT SKET RKET 
  SECTKET NAME STRINGCONST NUMBER TRUE FALSE

and the second is from the set of items which may start: a command, namely:

  TEST FOR IF UNLESS UNTIL WHILE GOTO RESULTIS 
  CASE DEFAULT BREAK RETURN FINISH SECTBRA 
  RBRA VALOF LV RV NAME

...

( ) [ ] § § are used to denote RBRA RKET SBRA SKET SECTBRA and SECTKET.

[0]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...