Why is this javascript object manipulated?

Question

Can anyone shed light on this behavior? and how could a be handled privately as a new object instance? Thanks

var a = {};

var b = function(obj) {
  obj.z = 10;
  return obj;
};

console.log("---");
console.log(a); // a = {}
b(a);
console.log(a); // a = {z: 10} -- why is a affected? it's not a = b(a);
(function(obj){
  obj.x = 9;
  console.log(obj);
})(a);
console.log(a); // a = {z:10, x: 9} -- a is also manipulated, why?

EDIT: Objects are accessed by reference therefore "a" is affected globally. Question is, in a Node.js scenario, these objects could be altered by different users entry points if the instance is not isolated / new. ideas on this?

Review this question http://stackoverflow.com/questions/122102/most-efficient-way-to-clone-an-object — Artyom Neustroev, May 24 '13 at 07:19
read this: [**JAVASCRIPT: PASSING BY VALUE OR BY REFERENCE**](http://snook.ca/archives/javascript/javascript_pass) — Grijesh Chauhan, May 24 '13 at 07:21
Object is always passed by reference, got it, but how can I create a new instance of that object, processing it without effecting the original object? — Sagish, May 24 '13 at 07:39

score 0 · Accepted Answer · answered May 24 '13 at 07:21

0

When you send the variable a as a parameter to a function, it's not a copy of the object in a that is sent to the function, but a reference to the object.

The parameter obj in the function will be a reference to the same object that the variable a points to. When you change obj in the function, the change affects the object itself. When you later use the variable a to look at the object, you see the changes.

answered May 24 '13 at 07:21

Guffa

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Makes sense, but how could "a" be handled privately as a new object instance, not effecting the reference? – Sagish May 24 '13 at 07:36
@SagiIsha: To get separate instances you have to actually create two separate instances, there is no way to automatically clone objects. Some libraries have methods that you can use to clone objects, like the `extend` method in jQuery. – Guffa May 24 '13 at 07:49

Why is this javascript object manipulated?

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