Do parentheses prevent semicolon insertion?

Question

Say that I want to set a bunch of variables equal to null (and don't want to use an array/loop structure) or maybe I just want to write a large boolean expression across multiple lines. Does an unclosed parenthetical prevent semicolon insertion in such a case? E.g.

some_variable = another_variable = yet_another_variable = (
    oh_look_a_parenthesis_above_me = hey_heres_another_variable) = (
    and_for_some_reason_another = last_one) = null;

Or

if(test_for_some_complex_expr && another_test || (
    but_maybe_this_one && or_this_one)) {
    // ...
}

And how does this compare versus using && or || or = to group expressions over line breaks? I.e., would this always work too?

some_variable = another_variable = 
    a_variable_after_a_line_break = and_one_more;

while(test_for_an_expr && another_test || 
    (an_expr_here && and_an_expr_here)) {
    // ...
}

I'm looking for the way that is most standard across all browsers (including IE6+).

Answer 1

Semicolon insertion only happens if you have code which would be a syntax error without the semicolon. In your case the expression is perfectly valid, so you don't need to worry about semicolon insertion - parentheses or not.

An example where semicolon insertion will happen:

var a = 1
var b = 2

In the above case, a semicolon is inserted at the line break, but only because it is a syntax error to write:

var a = 1 var b = 2

but it is perfectly valid to write:

var a = 1; var b = 2

The rules get tricky because there are some instances in JavaScript syntax where line breaks are NOT allowed. For example a line break is NOT allowed between the 'return' keyword and a value to return. So this is a syntax error:

return
  17;

But the way semicolon insertion "fixes" this error is by inserting a semicolon like this:

return;
  17;

Which is probably not what the writer intended! In that particular case, a parenthesis can be used to prevent semicolon insertion:

return (
   17);

Because it only between the return keyword and the start of the expression that line break is disallowed. Inside an expression it is not a problem.