Function.getMetadata

Function.getMetadata.js

(function () {
    // Reading Function Metadata
    // =========================
    //
    // !!!!! DO NOT USE ANY OF THIS CODE FOR ANY PURPOSE IT WILL EAT YOU KIDS
    //  
    // Because `Function.prototype.toString()` returns something like
    // function source-code, we can parse it for metadata like the names of
    // the formal arguments or the name of the function.  
    //
    // From Ecma-262 15.3.4.2 'Function.prototype.toString()' 
    //
    //     > An implementation-dependent representation of the function is 
    //     > returned. This representation has the syntax of a 
    //     > `FunctionDeclaration`. Note in particular that the use and placement of 
    //     > white space, line terminators, and semicolons within the 
    //     > representation String is implementation-dependent
    // 
    // So strictly speaking, I'm pretty sure we can't rely on this behaviour at all
    // in any context, but... it *seems* to work. ^_^ ;;;

    var function_pattern, function_to_string;

    Function.getMetadata = function (f) {
        /*jshint eqnull: true */
        var match = function_pattern.exec( function_to_string.call(f) );

        if (! match) throw "YOU NEVER SHOULD HAVE DONE THIS";

        return {
            args: match[2] == null ? [] : match[2].replace(/\s+/g, '').split(','),
            name: match[1].length > 0 ? match[1] : null
        };
    }; 

    // If you call this on a non-function it should throw a `TypeError` immediately
    function_to_string = (function (){}).toString;

    // This RegExp is used to "parse" the head of a function according to this grammar:
    //
    //     'function' <symbol> '(' (<symbol> [',' <symbol>]* )? ')'
    //
    // match[1] should contain the name (or empty string)
    // match[2] should contain the args (or null)
    function_pattern = /^\s*function\s*(\w*)\s*\(\s*(\w+(\s*,\s*\w+)*)?\s*\)/;
}());