Reading value from console interactively

Question

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 gt      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

User · Answer

This is overcomplicated  An easier version of   var rl   require  readline    rl createInterface    etc   would be to use  var rl   require  readline-sync      then it will wait when you use  rl question  string      then it is easier to repeat  for example   var rl   require  readline-sync    for let i 0 i lt 10 i          var ans   rl question  What  s your favourite food         console log  I like   ans   too

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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   gt      content    d toString         stdin addListener  end        gt      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

User · Answer

Please use readline-sync  this lets you working with synchronous console withouts callbacks hells  Even works with passwords    x000D   x000D  var favFood   read question  What is your favorite food       x000D    hideEchoBack  true    The typed text on screen is hidden by      default    x000D      x000D   x000D   x000D

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Blocking readline unblocked behaviour  Imagine you have three questions to be answered from the console  as you now know this code will not run because readline standard module has  unblocked  behaviour say each rl question is an independent thread so this code will not run    use strict    var questionaire    First Question          Second Question          Third Question           function askaquestion question    const readline   require  readline     const rl   readline createInterface       input  process stdin  output process stdout           rl question question 0   function answer        console log answer       question 1    answer      rl close              var i 0    for  i 0  i  lt  questionaire length  i      askaquestion questionaire i       console log  Results   questionaire      Running output   node test js Third Question  Results       First Question                Second Question                Third Question                    lt --- the last question remain unoverwritten and then the final line of the program is shown as the threads were running waiting for answers  see below  aaa         lt --- I responded with a single  a  that was sweeped by 3 running threads a         lt --- Response of one thread  a         lt --- Response of another thread  a         lt --- Response of another thread  there is no order on threads exit    The proposed solution uses an event emitter to signal the end of an unblocking thread  and includes the loop logic and end of program into its listener function    use strict    var questionaire    First Question          Second Question          Third Question              Introduce EventEmitter object const EventEmitter   require  events     class MyEmitter extends EventEmitter      const myEmitter   new MyEmitter    myEmitter on  continue        gt      console log  continue         i    if  i lt  questionaire length  askaquestion questionaire i  myEmitter         add here relevant loop logic            else console log  end of loop  nResults   questionaire            function askaquestion p question p my Emitter       add a parameter to include my Emitter const readline   require  readline     const rl   readline createInterface       input  process stdin  output process stdout           rl question p question 0   function answer        console log answer       p question 1    answer      rl close        myEmitter emit  continue          Emit  continue  event after the question was responded  detect end of unblocking thread              var i 0    for  i 0  i  lt  questionaire length  i      askaquestion questionaire i  myEmitter        var i 0  askaquestion questionaire 0  myEmitter             entry point to the blocking loop      console log  Results   questionaire       lt - moved to the truly end of the program   Running output   node test2 js First Question  1 1 continue    Second Question  2 2 continue    Third Question  3 3 continue    done  Results       First Question      1          Second Question      2          Third Question      3

User · Answer

I have craeted a little script for read directory and write a console name new file  example   name txt    and text into file   const readline   require  readline    const fs   require  fs     const pathFile   fs readdirSync        const file   readline createInterface     input  process stdin    output  process stdout      file question  Insert name of your file      f    gt      console log  File is    f toString   trim       try      file question  Insert text of your file      d    gt          console log  Text is    d toString   trim           try           if f                   if  fs existsSync f                   file exists             console log  file exist                return file close               else                save file             fs writeFile f  d   err    gt                    if  err  throw err                  console log  The file has been saved                     file close                                         else              file empty            console log  Not file is created               console log pathFile             file close                      catch err            console error err           file close                       catch err       console log err       file close

User · Answer

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

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I believe this deserves a modern async-await answer  assuming node  gt   7 x is used  The answer still uses ReadLine  question but wraps it so that the while  done     is possible  which is something the OP asks about explicitely  var cl   readln createInterface  process stdin  process stdout    var question   function q        return new Promise   res  rej    gt            cl question  q  answer   gt                res answer                          and then an example usage  async function main         var answer      while   answer     yes              answer   await question  Are you sure                console log   finally you are sure            leads to following conversation Are you sure  no Are you sure  no Are you sure  yes finally you are sure   Edit  In order to properly end the input  call cl close     at the end of the script

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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    gt      console log  Thank you for your valuable feedback    answer     rl close          More information here

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My approach to this would be to use async generators   Assuming you have an array of questions    const questions              How are you today              What are you working on              What do you think of async generators             In order to use the await keyword  you must wrap your program into an async IIFE    async      gt         questions Symbol asyncIterator    async function                const stdin   process openStdin            for  const q of this                   The promise won t be solved until you type something             const res   await new Promise  resolve  reject    gt                    console log q                   stdin addListener  data   data   gt                        resolve data toString                        reject  err                                                   yield  q  res                          for await  const res of questions            console log res             process exit 0          Expected results   How are you today   good    How are you today      good n    What are you working on         What are you working on         n    What do you think about async generators   awesome    What do you think about async generators      awesome n      If you want to get questions an answers altogether  you can achieve this with a simple modification   const questionsAndAnswers            for await  const res of questions               console log res          questionsAndAnswers push res             console log questionsAndAnswers                   How are you today      good n             What are you working on         n             What do you think about async generators      awesome n

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A common use case would probably be for the app to display a generic prompt and handle it in a switch statement   You could get a behaviour equivalent to a while loop by using a helper function that would call itself in the callback   const readline   require  readline    const rl   readline createInterface process stdin  process stdout    function promptInput  prompt  handler        rl question prompt  input   gt                if  handler input      false                        promptInput prompt  handler                     else                       rl close                         promptInput  app gt     input   gt        switch  input                case  my command                  handle this command             break          case  exit               console log  Bye                 return false              You could pass an empty string instead of  app gt    if your app already prints something to the screen outside of this loop

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I recommend using Inquirer  since it provides a collection of common interactive command line user interfaces   const inquirer   require  inquirer     const questions        type   input     name   name     message   What s your name         const answers   await inquirer prompt questions   console log answers

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Easiest way is to use readline-sync  It process one by one input and out put   npm i readline-sync   eg    var firstPrompt   readlineSync question  Are you sure want to initialize new db  This will drop whole database and create new one  Enter   yes no       if  firstPrompt      yes         console log  --firstPrompt--   firstPrompt      startProcess     else if  firstPrompt      no         var secondPrompt   readlineSync question  Do you want to modify migration   Enter   yes no          console log  secondPrompt    secondPrompt      startAnother     else       console log  Invalid Input       process exit 0

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Here s a example   const stdin   process openStdin    process stdout write  Enter name      stdin addListener  data   text   gt      const name   text toString   trim     console log  Your name is      name     stdin pause      stop reading      Output   Enter name  bob Your name is  bob

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I ve used another API for this purpose    var readline   require  readline    var rl   readline createInterface process stdin  process stdout   rl setPrompt  guess gt      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

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I had to write a  tic-tac-toe  game in Node that took input from the command line  and wrote this basic async await block of code that did the trick   const readline   require  readline    const rl   readline createInterface     input  process stdin    output  process stdout      async function getAnswer  prompt      const answer   await new Promise  resolve  reject    gt       rl question    prompt  n    answer    gt          resolve answer                 return answer    let done   false const playGame   async      gt      let i   1   let prompt    Question    i   enter  q  to quit    while   done        i    1     const answer   await getAnswer prompt      console log    answer        prompt   processAnswer answer  i        rl close      const processAnswer    answer  i    gt         this will be set depending on the answer   let prompt    Question    i   enter  q  to quit       if answer      q   then quit   if  answer      q         console log  User entered q to quit       done   true     return          parse answer       if answer is invalid  return new prompt to reenter       if answer is valid  process next move       create next prompt   return prompt    playGame

[node.js] Reading value from console, interactively

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