方法1

function clone(obj){
	var o;
	if(typeof obj == "object"){
		if(obj === null){
			o = null;
		}else{
			if(obj instanceof Array){
				o = [];
				for(var i = 0, len = obj.length; i < len; i++){
					o.push(clone(obj[i]));
				}
			}else{
				o = {};
				for(var k in obj){
					o[k] = clone(obj[k]);
				}
			}
		}
	}else{
		o = obj;
	}
	return o;
}

方法2 

function clone(obj){
    var o, obj;
    if (obj.constructor == Object){
        o = new obj.constructor(); 
    }else{
        o = new obj.constructor(obj.valueOf()); 
    }
    for(var key in obj){
        if ( o[key] != obj[key] ){ 
            if ( typeof(obj[key]) == 'object' ){ 
                o[key] = clone(obj[key]);
            }else{
                o[key] = obj[key];
            }
        }
    }
    o.toString = obj.toString;
    o.valueOf = obj.valueOf;
    return o;
}

方法3

function clone(obj){
	function Fn(){}
	Fn.prototype = obj;
	var o = new Fn();
	for(var a in o){
		if(typeof o[a] == "object") {
			o[a] = clone(o[a]);
		}
	}
	return o;
}