Simple method for calculating the length of an associative array (i.e. object). Counts the first-level child properties only.

objectsize.js

/**
 * Object Size - a simple utility function for returning the length of an associative array (i.e. object)
 * 
 * Counts the first-level direct child properties of the object and returns the count
 * 
 * @author Steven Wiggins
 * @date 2/4/2014
 * @version 0.2
 */
;(function() {
    
    Object.prototype.size = function() {

        var total = 0, prop;
        
        // this becomes trivial if the engine supports the Object.keys() function
        if( Object.keys ) {
            
            return Object.keys( this ).length;
            
        }

        // otherwise, we do it the old-fashioned way
        for( prop in this ) {

            this.hasOwnProperty( prop ) && total++;

        }

        return total;

    };
    
}());