stdout write with Nodejs

Question

I'm getting started with some modern Javascript, I decided to use Nodejs because it appears to be the most popular framework for JS on the desktop at the moment, I don't understand both why my code doesn't work and the associated error message that I get.

Consider this snippet

var a = 5;
var func = function(){return arguments.length;};
process.stdout.write(+func(1,2,3,a));

It doesn't work and it generates the following error message

net.js:612
    throw new TypeError('invalid data');
          ^
TypeError: invalid data
    at WriteStream.Socket.write (net.js:612:11)
    at Object.<anonymous> (var_1.js:3:16)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:902:3

I'm a C/C++ programmer and this is absolutely cryptic to me, moreover I used a + before invoking func to make sure that the result is an integer, so why write is complaining at all ?

After some nonsense adding a + '\n' makes this code work

var a = 5;
var func = function(){return arguments.length;};
process.stdout.write(+func(1,2,3,a) + '\n');

Anyone can explain what's going on ?

Answer 1

The 1st argument given to .write() is expected to be a String or Buffer. Numbers aren't allowed.

process.stdout.write(func(1,2,3,a).toString());

process.stdout.write(String(func(1,2,3,a)));

The Addition operator (a + b) does this conversion implicitly when concatenating '\n'.

Answer 2

You can only write strings or Buffers to sockets. (stdout is a socket.) As a integer is not a string or a buffer, trying to write it to stdout is an error.

Concatenating a string to an integer coerces (converts) the integer to a string, which is why it worked. You could concatenate an empty string (i+'') or call the integer's toString method.