Unable to figure out whether to use "," or "+" in console.log in node.js

This is the config.json file:

{
"username": "myname",
"api-key": "test",
"name": "testname",
"version": 1
}

This is the node.js file

var fs=require("fs");
console.log("Start");
var contents=fs.readFileSync("config.json");
console.log("Contents: " +contents);
var config=JSON.parse(contents);
console.log("Username: ", config.username);

Now whether I use

console.log("Username: ", config.username); 

or I use

console.log("Username:" +config.username);

I get the same result in the output. However it gives different results while logging other variables. Unable to get when "," is used and when "+" is used. Any pointers?

If you use + then that is a concatenation operator, and you pass a single string (or number) to log().

If you use a ,, then you are passing multiple arguments.

If you pass multiple arguments, and you aren't using a formatting string, then they will each get logged via inspect.

See the documentation for console.log and util.inspect for more details.

The difference is that the + operator varies from a concatenation operator if one or more of the variables is a string, versus an addition operator if both variables are non-stringified numbers. The , separator always converts each variable to a string separately and logs them separately.