Why doesn't this crazy brackety Javascript cause a syntax error? - Stack Overflow

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I was playing around with some Javascript snippets today and noticed that this code would actually run:

{{for(var i = 0; i < 3; i++) {{{{
  alert(i);
}}}}}}

You can try it out for yourself on jsFiddle.

Why does this run without any syntax errors? What do the repeated brackets mean? Does Javascript just ignore repeated curly braces?

I was playing around with some Javascript snippets today and noticed that this code would actually run:

{{for(var i = 0; i < 3; i++) {{{{
  alert(i);
}}}}}}

You can try it out for yourself on jsFiddle.

Why does this run without any syntax errors? What do the repeated brackets mean? Does Javascript just ignore repeated curly braces?

• javascript

Share Improve this question Follow asked Jun 28, 2012 at 20:18 Peter OlsonPeter Olson 143k4949 gold badges208208 silver badges249249 bronze badges 8

• 13 I get the error "too brackety." Do you think something's wrong with my interpreter? – Daniel Commented Jun 28, 2012 at 20:20
• @Daniel You should disable some of the strictness options on jsLint. – Peter Olson Commented Jun 28, 2012 at 20:21
• Also, you might be interested in stackoverflow./q/8618270/707111. – Ry- ♦ Commented Jun 28, 2012 at 20:22
• 2 I guess the point is "why plicate the spec?" - If someone wants to throw in tons of useless curly-braces, so be it. Otherwise, you're requiring the implementers of JavaScript interpreters to check for unnecessary levels of block scopes. Then IE would of course do it all weird and then nothing works right.. – Mike Christensen Commented Jun 28, 2012 at 20:28
• 2 In what way is this "too localized"? Argh, people always want to close the best questions. – Ry- ♦ Commented Jun 30, 2012 at 3:15

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3 Answers 3

Sorted by: Reset to default 12

It creates a new block, which is effectively useless¹ because JavaScript doesn't have block scope².

_{¹ This is a beautiful oxymoron.
² Yet.}

{ x++; } is a "Block Statement".

{{{ x++; }}} is a block inside a block inside a block.

The code inside each block is executed. So adding extra {} around someting doesn't do anythng.

Brackets-within-brackets is just delineated blocks of code. Your sample could expand out to:

{
    {
        for(var i = 0; i < 3; i++)
        {
            {
                {
                    { 
                        alert(i); 
                    }
                }
            }
        }
    }
} 

which is silly, but fine

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