Lambda function syntax in JavaScript without curly braces

I just found out that the following (awesome) syntax is accepted by Firefox

f = function(x) x+1;
f(17) //gives 18

Does anyone know what the hell is going on here? Is this in any开发者_Go百科 standard? Do other browsers also accept it? (I tested IE 8 and it gave me syntax error)

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This isn't part of a standard. The documentation is at https://developer.mozilla.org/en/New_in_JavaScript_1.8#Expression_closures_%28Merge_into_own_page.2fsection%29

There's discussion about adding some syntax along these lines or even shorter to the standard. See http://wiki.ecmascript.org/doku.php?id=strawman:shorter_function_syntax

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The braces are being omitted, just as you can for other control structures that take a block (if,for). It's part of standard syntax for those, perhaps not for functions. One could check the spec I guess.

The convention is that if braces are omitted, the block is the following single statement (only one statement).

For example

if(x) g=1;

is equivalent to

if(x){ g=1; }

However, note that

if(x) g=1; f=2;

is NOT equivalent to

if(x){ g=1; f=2; }

it is actually

if(x){ g=1; } f=2;

I avoid the braceless construct, personally, since it can lead to maintainability problems when the code is modified by people who don't know how this works.