Simple concat two array of objects problem

plan_cookie = plan_cookie.concat(JSON.stringify(protect_plan_from_db));


alert("2.1 after CONCAT plan_cookie = " + JSON.stringify(plan_cookie));


/*


2.1 after CONCAT plan_cookie =
"[{"id":1,"productId":1,"planDescription":"No Protection Plan","originalPrice":0,"salePrice":0,"active":1},
{"id":2,"productId":1,"planDescription":"1 Year Extension Protection Plan","originalPrice":69.99,"salePrice":69.99,"active":1},
{"id":3,"productId":1,"planDescription":"2 Year Extension Protection Plan","originalPrice":89.99,"salePrice":89.99,"active":1},
{"id":4,"productId":1,"planDescription":"3 Year Extension Protection Plan","originalPrice":109.99,"salePrice":109.99,"active":1},
{"id":5,"productId":1,"planDescription":"4 Year Extension Protection Plan","originalPrice":129.99,"salePrice":129.99,"active":1}]
[{"id":6,"productId":3,"planDescription":"No Protection Plan","originalPrice":0,"salePrice":0,"active":1},
{"id":7,"productId":3,"planDescription":"1 Year Extension Protection Plan","originalPrice":79.99,"salePrice":79.99,"active":1},
{"id":8,"productId":3,"planDescription":"2 Year Extension Protection Plan","originalPrice":99.99,"salePrice":99.99,"active":1}]"


*/