Reading value from console, interactively

Problem

I thought to make an simple server http server with some console extension. I found the snippet to read from command line data.

  var i = rl.createInterface(process.stdin, process.stdout, null);
  i.question('Write your name: ', function(answer) {
    console.log('Nice to meet you> ' + answer);
    i.close();
    process.stdin.destroy();

  });

well to ask the questions repeatedly, i cant simply use the while(done) { } loop ? Also well if the server receives output at the question time, it ruins the line.

Problem courtesy of: Risto Novik

Solution

you can't do a "while(done)" loop because that would require blocking on input, something node.js doesn't like to do.

Instead set up a callback to be called each time something is entered:

var stdin = process.openStdin();

stdin.addListener("data", function(d) {
    // note:  d is an object, and when converted to a string it will
    // end with a linefeed.  so we (rather crudely) account for that  
    // with toString() and then trim() 
    console.log("you entered: [" + 
        d.toString().trim() + "]");
  });
Solution courtesy of: rob

Discussion

The Readline API has changed quite a bit since 12'. The doc's show a useful example to capture user input from a standard stream :

const readline = require('readline');

const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});

rl.question('What do you think of Node.js? ', (answer) => {
  console.log('Thank you for your valuable feedback:', answer);
  rl.close();
});

More information here.

Discussion courtesy of: Patrick.SE

@rob answer will work most of the times, but it might not work as you expect with long inputs.

That is what you should be using instead:

const stdin = process.openStdin();
let content = '';

stdin.addListener('data', d => {
  content += d.toString();
});

stdin.addListener('end', () => {
  console.info(`Input: ${content}`);
});

Explanation on why this solution works:

addListener('data') works like a buffer, callback will be called when it is full or/and its the end of input.

What about long inputs? A single 'data' callback will not be enough, hence it you will get your input split in two or more parts. That is often not convenient.

addListener('end') will notify us when the stdin reader is done reading our input. Since we have been storing the previous data, we can now read and process it all together.

Discussion courtesy of: zurfyx

Please use readline-sync, this lets you working with synchronous console withouts callbacks hells. Even works with passwords:

var favFood = read.question('What is your favorite food? ', {
  hideEchoBack: true // The typed text on screen is hidden by `*` (default). 
});

Discussion courtesy of: Arango

I've used another API for this purpose..

var readline = require('readline');
var rl = readline.createInterface(process.stdin, process.stdout);
rl.setPrompt('guess> ');
rl.prompt();
rl.on('line', function(line) {
    if (line === "right") rl.close();
    rl.prompt();
}).on('close',function(){
    process.exit(0);
});

This allows to prompt in loop until the answer is right. Also it gives nice little console.You can find the details @ http://nodejs.org/api/readline.html#readline_example_tiny_cli

Discussion courtesy of: Madhan

This recipe can be found in it's original form on Stack Over Flow.