jquery.isObject.js

jquery.isObject.js

(function(jQuery){

    var toString = Object.prototype.toString,
        hasOwnProp = Object.prototype.hasOwnProperty;

    jQuery.isObject = function( obj ) {
        if ( toString.call(obj) !== "[object Object]" )
            return false;
        
        //own properties are iterated firstly,
        //so to speed up, we can test last one if it is not own
            
        var key;
        for ( key in obj ) {}
        
        return !key || hasOwnProp.call( obj, key );
    }

})(jQuery);

what if the object's .toString is overridden?

Overridden Object.prototype.toString? That would be silly.

Please note that probably this code isn't what you want. It is outdated and updated one is integrated into jQuery core as jQuery.isPlainObject since version 1.4.

Ah, my mistake. You're right, overriding the prototype's method would be silly. :P