Simple nodejs example with multiple files - node.js

Question

I wrote very simple project on NodeJS. I want to make similarity to other language programming example, such as java. So I make: server.js, main.js and module (calc.js). Here are their code:
File server.js
var main = require('./main');
var http = require('http');
http.createServer(function(req, res){
main.main(req, res);
}).listen(8080, '127.0.0.1');
console.log('Server running at http://127.0.0.1:8080/');
File main.js
var calc = require('./calc');
exports.main = function(req, res){
var a = 5;
var b = 9;
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end(calc.Plus(a,b));
res.end(calc.Minus(a,b));
};
File calc.js
(function(){
module.exports.Plus = function(a, b){
return a+b;
};
module.exports.Minus = function(a, b){
return a-b;
};
}());
I run it on my server, and I got an error:
Server running at http://127.0.0.1:8080/
_http_outgoing.js:558
throw new TypeError('First argument must be a string or Buffer');
^
TypeError: First argument must be a string or Buffer
at ServerResponse.OutgoingMessage.end (_http_outgoing.js:558:11)
at Object.exports.main (D:\workspace\FirstNodeJS\main.js:7:6)
at Server. (D:\workspace\FirstNodeJS\server.js:5:7)
at emitTwo (events.js:106:13)
at Server.emit (events.js:191:7)
at HTTPParser.parserOnIncoming [as onIncoming] (_http_server.js:546:12)
at HTTPParser.parserOnHeadersComplete (_http_common.js:99:23)
I am just a newbie with NodeJS.

Answer 1

res.end() expects the first argument to be a string or a buffer. You are passing a number. That is how it is described in the doc here.
You could do:
res.end(calc.Plus(a,b).toString());
Also, you can only call res.end() once for a given response. If you want to send multiple things as part of the response, you can either combine them all into a string before using res.end() or you can call res.write() multiple times and then finish it with res.end().

Answer 2

There are 2 issues to your problem.
First problem is that the `.write(...) API from NodeJS's response object takes in a string buffer or string.
Quote:
response.write(chunk[, encoding][, callback])
chunk < string > | < Buffer >
encoding
callback Returns:
See: https://nodejs.org/api/http.html#http_response_write_chunk_encoding_callback
Your calculation methods Plus and Minus are returning Integer. Hence you need to convert the Numbers to String before writting;
Example:
var calc = require('./calc');
exports.main = function(req, res){
var a = 5;
var b = 9;
res.writeHead(200, {'Content-Type': 'text/plain'});
var result = calc.Plus(a,b);
res.write(result.toString());
res.write("\n");
result = calc.Minus(a,b);
res.write(result.toString());
res.end();
};
Also, problem number 2 is that you should only call .end(...) once for each response object.
You should either build your result and then call it. Or call .write(...) as many times as you need and when you are happy then close the communication by calling .end(...).
Another thing, you might want to line break \n your results so that the output looks like;
If not it will be a one liner, 14-4.