Numeric triggers many syntax warnings in Firefox 40

[Jason Merrill]

Firefox 40 is currently the alpha/aurora/developer edition release. Loading numeric prints many warnings to the console of the form

SyntaxError: unreachable code after return statement numeric-1.2.6.js:3:54
SyntaxError: unreachable code after return statement numeric-1.2.6.js:5:26
SyntaxError: unreachable code after return statement numeric-1.2.6.js:3:51
SyntaxError: unreachable code after return statement numeric-1.2.6.js:5:31
SyntaxError: unreachable code after return statement numeric-1.2.6.js:3:69
SyntaxError: unreachable code after return statement numeric-1.2.6.js:3:52
SyntaxError: unreachable code after return statement numeric-1.2.6.js:3:86
SyntaxError: unreachable code after return statement numeric-1.2.6.js:5:39
SyntaxError: unreachable code after return statement numeric-1.2.6.js:4:47
SyntaxError: unreachable code after return statement numeric-1.2.6.js:6:39
SyntaxError: unreachable code after return statement numeric-1.2.6.js:4:32

Here's a jsbin that does nothing but include Numeric—you can open it in firefox 40 and check the console.

http://output.jsbin.com/qubolo

These are unfortunately not very easy to debug, because the line and column numbers appear to refer to generated code rather than the actual source of numeric.

[Adán SDPC // asdpc.eth]

As read in MDN:

Automatic Semicolon Insertion
The return statement is affected by automatic semicolon insertion (ASI). No line terminator is allowed between the return keyword and the expression.

return
a + b;

is transformed by ASI into:

return; 
a + b;

Starting with Gecko 40 the console will warn "unreachable code after return statement".

Link: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/return