code:

x = { a:{ a1:1, a2:2 }, b:2 };
y = { a:{ a3:3 }, c:3 };
console.log("x is ",JSON.stringify(x));
console.log("y is ",JSON.stringify(y));
console.log("$.isObject(x) is ",$.isObject(x))
z = $.extend(true,{}, x, y);
console.log("execut: z = $.extend(true,{}, x, y);");
console.log("x is ",JSON.stringify(x)," <--should not be changed!");

output:

x is  {"a":{"a1":1,"a2":2},"b":2}
y is {"a":{"a3":3},"c":3}
$.isObject(x) is false
execut: z = $.extend(true,{}, x, y);
x is {"a":{"a1":1,"a2":2,"a3":3},"b":2} <-- should not be changed!