How to read user input in node.js for simple calculations - node.js

Question

How can I read user input from the command line in node.js for simple calculations? I'v been reading http://nodejs.org/api/readline.html#readline_readline and http://nodejs.org/api/process.html#process_process_stdin but I can't use my input for simple things like console.log(input). I know these are async functions, but I guess there must be a way of using the input for later calculations.
Do you have an example? Like a sum of two given numbers: input a and b and output a+b

Answer 1

Something like this?
var readline = require('readline');
var rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});
function processSum(number) {
// Insert code to do whatever with sum here.
console.log('The sum is', number);
}
rl.question('Enter a number: ', function (x) {
rl.question('Enter another number: ', function (y) {
var sum = parseFloat(x) + parseFloat(y);
processSum(sum)
rl.close();
});
});

Answer 2

You could write a reusable module like this:
// ask.js
const readline = require("readline");
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});
rl.pause();
function ask(question, cb = () => void 0) {
return new Promise(resolve => {
rl.question(question, (...args) => {
rl.pause();
resolve(...args);
cb(...args);
});
});
}
module.exports = ask;
And use it with multiple approaches everywhere:
Approach #1 (with async/await):
const ask = require("./ask");
(async () => {
const a = await ask("Enter the first number: ");
const b = await ask("Enter the second number: ");
console.log("The sum is", a + b);
})();
Approach #2 (with Promise):
const ask = require("./ask");
ask("Enter the first number: ")
.then(a => {
ask("Enter the second number: ")
.then(b => {
console.log("The sum is", a + b);
});
});
Approach #3 (with callback):
const ask = require("./ask");
ask("Enter the first number: ", a => {
ask("Enter the second number: ", b => {
console.log("The sum is ", a + b);
});
});