//create primtives var N = 5; var S = 'foo'; var B = true; //add properties to primitives, that get destroyed when wrapper is trashed N.test = 'test'; S.test = 'test'; B.test = 'test'; //verify that non of these properties remain. console.log(N.test); //logs undefined console.log(S.test); //logs undefined console.log(B.test); //logs undefined