Those are the JavaScript 1.8 (FF-only) "expression closures" the author mentions. JavaScript 1.8 introduces a succinct syntax for anonymous functions: func

Those are the JavaScript 1.8 (FF-only) "expression closures" the author mentions. JavaScript 1.8 introduces a succinct syntax for anonymous functions: function (a, b, c) a + b * c; which is the same as function (a, b, c) { return a + b * c; } Of course, this syntax breaks down if you want to return an object literal from your anonymous function. Curly braces are too overloaded in JS! Adding parentheses disambiguates between the new and the old function syntax.