Date.prototype.getDayOfMonth = function(Mm){ 
 				var Feb = (this.getFullYear() % 4 == 0)?29:28; 
 				var aM = new Array(31, Feb , 31, 30, 31, 30, 31, 31, 30, 31, 30, 31); 
 				return (typeof Mm == 'undefined')?aM[this.getMonth()-1]:aM[Mm-1]; 
 			}; 
 			Date.prototype.getDateOfPreMonth = function(){ 
 				 
 				return new Date( 
 								(this.getMonth() == 0)?(this.getFullYear()-1):this.getFullYear() , 
 								(this.getMonth() == 0)?11:this.getMonth() ,	 
 								this.getDayOfMonth( 
 												   (this.getMonth() == 0)?11:(this.getMonth()-1)  
 													 <= 
 												   this.getDate() 
 												   )?this.getDate(): 
 												   this.getDayOfMonth( 
 														(this.getMonth() == 0)?11:(this.getMonth()-1) 
 																	 ) 
 								 
 								); 
 			}; 
 			var d = new Date().getDateOfPreMonth(); 
 			alert(d);