undefined on server console after make-runnable-output - node.js

Question

I have created a simple html application on nodejs. Here is the code os server.ts
import express = require('express');
import http = require('http');
import path = require('path');
import cookieParser = require('cookie-parser');
export class Server {
static startServer() {
let app = express();
app.use(cookieParser());
app.use(express.static(__dirname + "/public"));
let server = http.createServer(app);
server.listen(7000, () => {
console.log('Up and running on port : ' + 7000);
});
}
}
exports.startServer = Server.startServer;
// Call a module's exported functions directly from the command line.
require('make-runnable');
I have used make-runnable module to run exported functions directly from the command line. And this is my start script in package.json
"start": "concurrently \"tsc --watch \" \"nodemon server.js startServer\""
the application is working fine, but this is printing undefined on the screen that annoying and this should be solved.
[1] [nodemon] restarting due to changes...
[1] [nodemon] starting `node server.js startServer`
[1] Up and running on port : 7000
[1] --------make-runnable-output--------
[1] undefined
[1] ------------------------------------
[0] 4:08:52 PM - Compilation complete. Watching for file changes.
What is the reason for this?

Answer 1

Solution
The make-runnable package provides you with the ability to clear the output frame by import the "custom" module and specifying a boolean value for printOutputFrame. Rather than require('make-runnable'), use:
require('make-runnable/custom')({
printOutputFrame: false
})
However, this doesn't remove the "undefined" (or output) message because make-runnable is expecting some return value to log as it resolves the promise.
Instead, return some value from your function for Bluebird (or make-runnable) to print on its own:
static startServer() {
let app = express();
app.use(cookieParser());
app.use(express.static(__dirname + "/public"));
let server = http.createServer(app);
- server.listen(7000, () => {
- console.log('Up and running on port : ' + 7000);
- });
+ server.listen(7000)
+ return 'Up and running on port : ' + 7000;
}
Note: I haven't verified that this won't cause the server to stop listening, but this is rather illustrating what the package will expect from your function.
Explanation
*Bit of an older question but I came across the same issue recently so I figured I'd provide a solution.
The reason why "undefined" is being printed is that it's expecting some return value from the function that you're calling. Consider this snippet of a function (that I was working on and ran across this issue):
generate: function() {
// ... some preliminary code
fs.writeFile(file, modifiedFileData, error => {
if (error) throw error
console.log('App key generated successfully.')
})
}
Output:
$ node utils/EncryptionKey.js generate
--------make-runnable-output--------
undefined
------------------------------------
App key generated successfully.
Done in 0.27s.
By default, I just want that message to be logged to the console. Without make-runnable it worked fine since I initially just ran the function, but wanted to put this into an export. Looking at the source code (engine.js) for make-runnable, the following function:
function printOutput(returnValue) {
Bluebird.resolve(returnValue)
.then(function (output) {
if (options.printOutputFrame) {
console.log('--------make-runnable-output--------');
}
console.log(output);
if (options.printOutputFrame) {
console.log('------------------------------------');
}
}).catch(printError);
}
expects some return value, since Bluebird wraps the function you're executing as a promise. I instead changed my initial code to:
generate: function () {
// ... some preliminary code
fs.writeFile(file, modifiedFileData, error => {
if (error) throw error
return true
})
return 'App key generated successfully.'
}
and removed the "undefined" value, and printed my app key message.
Output:
$ node utils/EncryptionKey.js generate
App key generated successfully.
Done in 0.26s.