Question

I wonder how memory is managed in V8. Take a look at this example:

function requestHandler(req, res){
  functionCall(req, res);
  secondFunctionCall(req, res);
  thirdFunctionCall(req, res);
  fourthFunctionCall(req, res);
};

var http = require('http');
var server = http.createServer(requestHandler).listen(3000);

The req and res variables are passed in every function call, my question is:

1. Does V8 pass this by reference or does it make a copy in memory?

2. Is it possible to pass variables by reference, look at this example.

   var args = { hello: 'world' };
   
   function myFunction(args){
     args.newHello = 'another world';
   }
   
   myFunction(args);
   console.log(args);
   

   The last line, console.log(args); would print:

   "{ hello: 'world', newWorld: 'another world' }"
   

Thanks for help and answers 🙂

Answer 1

That’s not what pass by reference means. Pass by reference would mean this:

var args = { hello: 'world' };

function myFunction(args) {
  args = 'hello';
}

myFunction(args);

console.log(args); //"hello"

And the above is not possible.

Variables only contain references to objects, they are not the object themselves. So when you pass a variable that is a reference to an object, that reference will be of course copied. But the object referenced is not copied.

---

var args = { hello: 'world' };

function myFunction(args){
  args.newHello = 'another world';
}

myFunction(args);
console.log(args); // This would print:
    // "{ hello: 'world', newHello: 'another world' }"

Yes that’s possible and you can see it by simple running the code.