display only value fields from the msg.payload in

I am working on node red (SNMP).

When I deploy, I have the output below:

[ { "oid": "1.3.6.1.2.1.10.21.1.2.1.1.2.1.26", "type": 2, "value": 104, "tstr": "Integer" }, { "oid": "1.3.6.1.2.1.10.21.1.2.1.1.2.2.27", "type": 2, "value": 104, "tstr": "Integer" }, { "oid": "1.3.6.1.2.1.10.21.1.2.1.1.2.10.28", "type": 2, "value": 1, "tstr": "Integer" }, { "oid": "1.3.6.1.2.1.10.21.1.2.1.1.2.11.29", "type": 2, "value": 1, "tstr": "Integer" }, { "oid": "1.3.6.1.2.1.10.21.1.2.1.1.2.12.30", "type": 2, "value": 1, "tstr": "Integer" }, { "oid": "1.3.6.1.2.1.10.21.1.2.1.1.2.13.31", "type": 2, "value": 1, "tstr": "Integer" }, { "oid": "1.3.6.1.2.1.10.21.1.2.1.1.2.14.32", "type": 2, "value": 101, "tstr": "Integer" }, { "oid": "1.3.6.1.2.1.10.21.1.2.1.1.2.15.38", "type": 2, "value": 1, "tstr": "Integer" }, { "oid": "1.3.6.1.2.1.10.21.1.2.1.1.2.100.39", "type": 2, "value": 101, "tstr": "Integer" }, { "oid": "1.3.6.1.2.1.10.21.1.2.1.1.2.101.40", "type": 2, "value": 101, "tstr": "I ....

so I want to display all of the values from this output (104, 104, 1, 1 ....)

I am writing this function:

for(var i =0; i<Object.keys(msg.payload).length;i++)
{  
  msg.payload+=msg.payload[Object.keys(msg.payload)[i]].value;
}
return msg;

but I have an error:

TypeError: Object.keys called on non-object

any idea?

The problem is that your for loop is modifying msg.payload on each iteration - and because it is doing a += it is turning it into a String. That means the second time through the loop, msg.payload is no longer the object it was at the start so the Object.keys call fails.

You should build up your result in a new variable and set msg.payload at the end:

var result = [];
var keys = Object.keys(msg.payload);
for(var i =0; i<keys.length;i++)
{  
  result.push(msg.payload[keys[i]].value);
}
// At this point, result is an array of the values you want
// You can either return it directly with:
//    msg.payload = result;

// or, if you want a string representation of the values as a
// comma-separated list:
//    msg.payload = result.join(", ");

return msg;