$.isPlainObject inconsistent

[rwaldron]

As documented in this fiddle, $.isPlainObject() is evaluating inconsistently across browsers.

[rwaldron]

Initially reported by jaubourg here: #7743

[rwaldron]

 http://jsfiddle.net/rwaldron/UUvte/9/

[dmethvin]

I thought we accepted that host objects might break this way, kind of like how we don't support $.isFunction(window.alert). Or is the needsdocs here just to say we need to document that fact?

[rwaldron]

Dave, yes - there are too many host objects that have too many inconsistencies for the library to robustly feature detect (without adding garbage regular expressions) - the needsdocs tag is to document this.

[shane@…]

	isPlainObject: function( obj ) {
		// Must be an Object.
		// Because of IE, we also have to check the presence of the constructor property.
		// Make sure that DOM nodes and window objects don't pass through, as well
		if ( !obj || jQuery.type(obj) !== "object" || obj.nodeType || jQuery.isWindow( obj ) ) {
			return false;
		}

		// Not own constructor property must be Object
		if ( obj.constructor &&
			!hasOwn.call(obj, "constructor") &&
			!hasOwn.call(obj.constructor.prototype, "isPrototypeOf") ) {
			return false;
		}

		// Own properties are enumerated firstly, so to speed up,
		// if last one is own, then all properties are own.

		var key;
		for ( key in obj ) {
		  if(!hasOwn.call( obj, key )){
		    return false;
		  }
		}

		return key === undefined;
	}

[addyosmani]

Documentation updated:  http://api.jquery.com/jQuery.isPlainObject/