So I'm using this example code from the NodeJS docs:

const readline = require('readline');
const rl = readline.createInterface(process.stdin, process.stdout);
console.log("Hello!");
rl.setPrompt('OHAI> ');
rl.prompt();

rl.on('line', (line) => {
  switch(line.trim()) {
    case 'hello':
      console.log('world!');
      break;
    default:
      console.log('Say what? I might have heard `' + line.trim() + '`');
      break;
  }
  rl.prompt();
}).on('close', () => {
  console.log('Have a great day!');
  process.exit(0);
});

I'm on Windows, running NodeJS 6.0.0. When I run the file, it writes "Hello!", followed by the first "OHAI> ". So far so good. Now I try writing an arbitrary "asd". When I press enter, one of two things happens:

1. It prints:

asd

Say what? I might have heard 'asd'

OHAI>

2. It prints

Say what? I might have heard 'asd'

OHAI>

This only happens on the first input line. It seems to be pletely random, however if, after I type node test.js, I press enter fast enough, sometimes I get a newline before the first "OHAI> " and it doesn't print my arbitrary input.

Is there something wrong with the example? Is it a bug in NodeJS? Even if it can't be fixed, I'd be relieved to know what causes it, since I've been pulling my hairs out for hours now.

So I'm using this example code from the NodeJS docs:

const readline = require('readline');
const rl = readline.createInterface(process.stdin, process.stdout);
console.log("Hello!");
rl.setPrompt('OHAI> ');
rl.prompt();

rl.on('line', (line) => {
  switch(line.trim()) {
    case 'hello':
      console.log('world!');
      break;
    default:
      console.log('Say what? I might have heard `' + line.trim() + '`');
      break;
  }
  rl.prompt();
}).on('close', () => {
  console.log('Have a great day!');
  process.exit(0);
});

I'm on Windows, running NodeJS 6.0.0. When I run the file, it writes "Hello!", followed by the first "OHAI> ". So far so good. Now I try writing an arbitrary "asd". When I press enter, one of two things happens:

1. It prints:

asd

Say what? I might have heard 'asd'

OHAI>

2. It prints

Say what? I might have heard 'asd'

OHAI>

This only happens on the first input line. It seems to be pletely random, however if, after I type node test.js, I press enter fast enough, sometimes I get a newline before the first "OHAI> " and it doesn't print my arbitrary input.

Is there something wrong with the example? Is it a bug in NodeJS? Even if it can't be fixed, I'd be relieved to know what causes it, since I've been pulling my hairs out for hours now.

• javascript
• node.js
• user-input
• readline

2 Answers 2

This should solve the issue.

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

I'm still not sure why this happens, but I've found a way around it. It's a bit ugly, but it does the job.

var rl;
function cli() {
    const readline = require('readline');
    rl = readline.createInterface(process.stdin, process.stdout);
    rl.prompt();
    rl.on('line', exec_cmd);
    rl.on('close', () => {
        console.log('And now we part pany.');
        process.exit(0);
    });
}
function fixfunc() {
    //get first input
    var input = process.stdin.read();
    if (input == null)
        return;
    input = input.toString("utf-8");
    //No longer needed, so remove the listener
    process.stdin.removeListener('readable', fixfunc);
    process.stdin.resume();
    //do whatever you want with the input
    exec_cmd(input);
    //Initialize readline and let it do its job
    cli();
}
process.stdin.pause();
process.stdin.on('readable', fixfunc);
process.stdout.write("> Wele, Commander!\n> ");

What this basically does, is pause stdin, get the first input, manually call the parsing function and then initalize readline and let it do its job.