NodeJS calling readline within a function - node.js

Question

I'm learning NodeJS and I encounter a basic issue. I'm trying to read a file line by line, and for each line I read to send an HTTP request to / + <the line> e.g.:
wlist.txt contents
line
line2
failed attempt:
const request = require('request') // for http request later
const readline = require('readline')
const fs = require('fs')
function fileLoader() {
const readInterface = readline.createInterface({
input: fs.createReadStream('C:\\etc\\code\\req\\wlist.txt'),
});
readInterface.on('line', function(line) {
return "test";
});
}
var aba = fileLoader();
console.log(aba); // undefined
My logic inserting fileLoader as a function and not "as is" is that I later on have a switch case that uses the file load to different purposes such as XML request or JSON request.. lets say:
switch (myArgs[0]) {
case 'json':
let myJSON = {username: 'val'};
request({
url: "http://192.168.1.2:3000",
method: "POST",
json: true,
body: myJSON
}, function (error, response, body){
console.log(response.headers)
console.log(response.body)
});
break;
case 'xml': .....
I'm fully aware theres something I missing, probably regarding async / promises or anything, but to really educate, may someone please go easy on me and show me the way? I've tried everything and just can't get a grasp of whats the problem..

Answer 1

I believe you would like to do something like this:
https://gist.github.com/EB-BartVanVliet/533d55eb17c97f2a12ed25f479786f4a
Essentially what I do is:
Parse the file, look for empty lines and remove those
I declare a async start function so that I can use await inside the for loop
Log the output

Answer 2

You can do simple like this:
var sendRequest = function (input) {
// Do whatever you want here
}
var lineReader = require('readline').createInterface({
input: require('fs').createReadStream('path_to_your_file')
});
lineReader.on('line', function (line) {
console.log('Line from file:', line);
sendRequest(line);
});

Answer 3

readline is asynchronous so chances are that console.log is being called before fileLoader has finished. Try using readline-sync if you are happy to block whilst the file is read.
Otherwise you should re-write so the the on('line',...) method performs the action you want to take with the line as it is read. (I think this is what you want - "read a file line by line, and for each line I read to send an HTTP request"). E.g.
on('line', (input) => { /* perform send http stuff/call function to do it */ } );
Or, if you only want to act when the whole file is read, you'll have to re-structure so that the file-read is wrapped in a promise (or use async/await).