Unexpected setting of context data in Function Node

General
1

Hi,
I'm new here (and new is NodeRED form me) so I don't know if my question is really a problem;
In a function node I placed this code:

var obj = flow.get("obj");
obj[0].a = "1";
return msg;

The problem is that the flow data change olso if in this function there isn't a flow.set(...) stantment

The flow variable 'obj' is created by an another function with this code:

var obj = [{a: "str1", b: 1, c: "11:00", d: "12:00"},
            {a: "str2", b: 2, c: "13:00", d: "14:00"},
            {a: "str3", b: 3, c: "15:00", d: "16:00"}]

flow.set("obj", obj);
msg.payload = obj;
return msg;

Anyone can explain me the reasons?

I thank those who will answer me in advance

Alan

2

Objects in javascript are passed by reference when you get the object from flow or global context it is exactly the same object (your variable is simply a reference to the original)

3

Hi Steve,
thank for the fast reply :grinning:
Is there a solution to avoid this?

Alan

4

It depends what you are trying to achieve.

If you wish to have a new clone that doesn't affect the object, there is a helper function RED.util.cloneMessage() you can use to make a copy before modifying it.

e.g...

var obj = RED.util.cloneMessage(flow.get("obj") || {});
5

Thank Steve,
in the meantime I found (and tried) this code:

var objTemp = JSON.parse(JSON.stringify(obj));

is also good as is or there are some important differences?

Alan

6

The helper function takes care of special cases. Also, i don't think the serialisation to string is performed in the helper function so should be faster / safer.

7

This topic was automatically closed 60 days after the last reply. New replies are no longer allowed.