Not able to declare a function in the console when brackets on the same line

Question

In the Chrome console, I executed the following function:

function getData_working(){ 
  return [
    {Category: "Category 1", Key: "Key 10", Value: 1},
    {Category: "Category 2", Key: "Key 10", Value: 1}
  ];
}

It does work and executing getData_working() afterwards produces the expected array with two objects. However, when I execute the following function (and I've actually copied the former, only changing the placement of the brackets, to make sure it isn't a typo), I get undefined.

function getData2_failing(){ 
  return 
    [{Category: "Category 1", Key: "Key 10", Value: 1},
    {Category: "Category 2", Key: "Key 10", Value: 1}];
}

What's happening here? How does someone explain this "bug" or "feature"?

Answer 1

You can't put return on its own line. Well, you can, but if you do, you will get a return value of undefined every time. This is because of how automatic semicolon insertion works.

• Forbidden LineTerminators: The following syntactic constructs forbid a newline (“LineTerminator”) at a certain position. If there is a newline at that position, a semicolon is inserted. The ECMAScript standard calls the grammar rules below restricted productions.

PostfixExpression
LeftHandSideExpression [no LineTerminator here] ++
LeftHandSideExpression [no LineTerminator here] --

ContinueStatement
continue [no LineTerminator here] Identifier? ;

BreakStatement
break [no LineTerminator here] Identifier? ;

ReturnStatement
return [no LineTerminator here] Expression? ;

ThrowStatement
throw [no LineTerminator here] Expression? ;

For PostfixExpression, the rationale is avoiding the modification of a value on the previous line. For continue, break, return and throw, the rationale is that if they are used without an argument, they should not refer to the next line if one forgets a semicolon.

_{source: http://www.2ality.com/2011/05/semicolon-insertion.html}

If you want the brackets on the next line, you need

return (
  [ ... ]
);

Or do like you've done in your original code

return [
  ...
];