How can I wait In Node js JavaScript l need to pause for a period of time

Question

I m developing a console script for personal needs  I need to be able to pause for an extended amount of time  but  from my research  Node js has no way to stop as required  It   s getting hard to read users    information after a period of time    I   ve seen some code out there  but I believe they have to have other code inside of them for them to work such as       setTimeout function            3000     However  I need everything after this line of code to execute after the period of time   For example           start of code     console log  Welcome to my console          some-wait-code-here-for-ten-seconds         console log  Blah blah blah blah extra-blah           end of code   I ve also seen things like      yield sleep 2000     But Node js doesn t recognize this   How can I achieve this extended pause

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let co   require  co    const sleep   ms   gt  new Promise res   gt  setTimeout res  ms     co function          console log  Welcome to My Console         yield sleep 3000       console log  Blah blah blah blah extra-blah          This code above is the side effect of the solving Javascript s asynchronous callback hell problem  This is also the reason I think that makes Javascript a useful language in the backend  Actually this is the most exciting improvement introduced to modern Javascript in my opinion  To fully understand how it works  how generator works needs to be fully understood  The function keyword followed by a   is called a generator function in modern Javascript  The npm package co provided a runner function to run a generator   Essentially generator function provided a way to pause the execution of a function with yield keyword  at the same time  yield in a generator function made it possible to exchange information between inside the generator and the caller  This provided a mechanism for the caller to extract data from a promise from an asynchronous call and to pass the resolved data back to the generator  Effectively  it makes an asynchronous call synchronous

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For more info on  yield sleep 2000      you should check Redux-Saga  But it is specific to your choice of Redux as your model framework  although strictly not necessary

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simple we are going to wait for 5 seconds for some event to happen  that would be indicated by done variable set to true somewhere else in the code  or when timeout expires that we will check every 100ms      var timeout 5000    will wait for 5 seconds or untildone     var scope   this    bind this to scope variable      function             if  timeout lt  0    scope done    timeout expired or done                       scope callback     some function to call after we are done                   else                       setTimeout arguments callee 100    call itself again until done             timeout -  100

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Simple and elegant sleep function using modern Javascript  function sleep millis        return new Promise resolve   gt  setTimeout resolve  millis        No dependencies  no callback hell  that s it  -     Considering the example given in the question  this is how we would sleep between two console logs   async function main         console log  Foo        await sleep 2000       console log  Bar       main      The  drawback  is that your main function now has to be async as well  But  considering you are already writing modern Javascript code  you are probably  or at least should be   using async await all over your code  so this is really not an issue  All modern browsers today support it   Giving a little insight into the sleep function for those that are not used to async await and fat arrow operators  this is the verbose way of writing it   function sleep millis        return new Promise function  resolve  reject            setTimeout function      resolve       millis               Using the fat arrow operator  though  makes it even smaller  and more elegant

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With ES6 supporting Promises  we can use them without any third-party aid   const sleep    seconds    gt        return new Promise  resolve  reject    gt            setTimeout resolve   seconds   1000                   We are not using  reject  anywhere  but it is good to    stick to standard signature    Then use it like this   const waitThenDo howLong  doWhat    gt        return sleep howLong  then doWhat        Note that the doWhat function becomes the resolve callback within the new Promise        Also note that this is ASYNCHRONOUS sleep  It does not block the event loop  If you need blocking sleep  use this library which realizes blocking sleep with the help of C   bindings   Although the need for a blocking sleep in Node like async environments is rare    https   github com erikdubbelboer node-sleep

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If you just need to suspend for testing purpose you current thread execution try this   function longExecFunc callback  count         for  var j   0  j  lt  count  j              for  var i   1  i  lt   1  lt  lt  30   i                  var q   Math sqrt 1  lt  lt  30                       callback      longExecFunc      gt    console log  done      5     5  6     whatever  Higher -- longer

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On Linux nodejs this works for me      const spawnSync   require  child process   spawnSync       var sleep   spawnSync  sleep    1 5      It is blocking  but it is not a busy wait loop   The time you specify is in seconds but can be a fraction  I don t know if other OS s have a similar command

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I ve recently created simpler abstraction called wait for to call async functions in sync mode  based on node-fibers   There is also a version based on upcoming ES6 Generators   https   github com luciotato waitfor  Using wait for  you can call any standard nodejs async function  as if it were a sync function  without blocking node s event loop    You can code sequentially when you need it  which is   I m guessing  perfect to simplify your scripts for personal use   using wait for your code will be   require  waitfor      in a fiber     start-of-code console log  Welcome to My Console     wait miliseconds 10 1000     defined in waitfor paralell-tests js - DOES NOT BLOCK console log  Blah blah blah blah extra-blah      endcode     Also any async function can be called in Sync mode  Check the examples

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You can use this www npmjs com package sleep  var sleep   require  sleep    sleep sleep 10      sleep for ten seconds

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This question is quite old  but recently V8 has added Generators which can accomplish what the OP requested   Generators are generally easiest to use for async interactions with the assistance of a library such as suspend or gen-run   Here s an example using suspend   suspend function           console log  Welcome to My Console         yield setTimeout suspend resume    10000      10 seconds pass       console log  Blah blah blah blah extra-blah            Related reading  by way of shameless self promotion   What s the Big Deal with Generators

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This is a moment js flavored module based on the dirty blocking approach suggested by  atlex2  Use this only for testing   const moment   require  moment     let sleep    secondsToSleep   1    gt        let sleepUntill   moment   add secondsToSleep   seconds        while moment   isBefore sleepUntill        block the process         module exports   sleep

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Since  javascript engine  v8  runs code based on sequence of events in event-queue  There is no strict that javascript exactly trigger the execution at after specified time  That is  when you set some seconds to execute the code later  triggering code is purely base on sequence in event queue  So triggering execution of code may take more than specified time   So Node js follows   process nextTick     to run the code later instead setTimeout    For example   process nextTick function        console log  This will be printed later

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function doThen conditional then timer        var timer   timer    1      var interval   setInterval function            if conditional                  clearInterval interval               then                     timer      Example usage  var counter   1  doThen      function             counter            return counter    1000             function             console log  quot Counter hit 1000 quot       1000 repeats later

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On Node 7 6 0 or higher  Node supports waiting natively   const sleep    waitTimeInMs    gt  new Promise resolve   gt  setTimeout resolve  waitTimeInMs      then if you can use async functions   await sleep 10000      sleep for 10 seconds   or   sleep 10000  then      gt         This will execute 10 seconds from now       On older Node versions  original answer   I wanted an asynchronous sleep that worked in Windows  amp  Linux  without hogging my CPU with a long while loop   I tried the sleep package but it wouldn t install on my Windows box   I ended up using   https   www npmjs com package system-sleep  To install it  type   npm install system-sleep   In your code    var sleep   require  system-sleep    sleep 10 1000      sleep for 10 seconds   Works like a charm

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Put the code that you want executed after the delay within the setTimeout callback   console log  Welcome to My Console     setTimeout function         console log  Blah blah blah blah extra-blah       3000

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The other answers are great but I thought I d take a different tact   If all you are really looking for is to slow down a specific file in linux    rm slowfile  mkfifo slowfile  perl -e  select STDOUT       1  while  lt  gt    print     sleep 1  if    ii     5     0      myfile  gt  slowfile   amp    node myprog slowfile  This will sleep 1 sec every five lines  The node program will go as slow as the writer   If it is doing other things they will continue at normal speed   The mkfifo creates a first-in-first-out pipe   It s what makes this work  The perl line will write as fast as you want   The    1 says don t buffer the output

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If you want to  code golf  you can make a shorter version of some of the other answers here   const sleep   ms   gt  new Promise resolve   gt  setTimeout resolve  ms      But really the ideal answer in my opinion is to use Node s util library and its promisify function  which is designed for exactly this sort of thing  making promise-based versions of previously existing non-promise-based stuff    const util   require  util    const sleep   util promisify setTimeout     In either case you can then pause simply by using await to call your sleep function   await sleep 1000      sleep for 1s 1000ms

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The shortest solution without any dependencies   await new Promise resolve   gt  setTimeout resolve  5000

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I put together  after having read the answers in this question  a simple function which can also do a callback  if you need that   function waitFor ms  cb      var waitTill   new Date new Date   getTime     ms     while waitTill  gt  new Date         if  cb        cb       else      return true

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Update Jan 2021  You can even do it in the Node REPL interactive using --experimental-repl-await flag   node --experimental-repl-await  gt  const delay   ms   gt  new Promise resolve   gt  setTimeout resolve  ms    gt  await delay 1000      waiting 1 second   A new answer to an old question  Today   Jan 2017 June 2019  it is much easier  You can use the new async await syntax  For example  async function init       console log 1     await sleep 1000     console log 2      function sleep ms      return new Promise  resolve    gt        setTimeout resolve  ms               For using async await out of the box without installing and plugins  you have to use node-v7 or node-v8  using the --harmony flag  Update June 2019  By using the latest versions of NodeJS you can use it out of the box  No need to provide command line arguments  Even Google Chrome support it today  Update May 2020  Soon you will be able to use the await syntax outside of an async function  In the top level like in this example await sleep 1000  function sleep ms      return new Promise  resolve    gt        setTimeout resolve  ms             The proposal is in stage 3  You can use it today by using webpack 5  alpha   More info   Harmony Flag in Nodejs  https   nodejs org en docs es6  All NodeJS Version for download  https   nodejs org en download releases

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This is a simple blocking technique   var waitTill   new Date new Date   getTime     seconds   1000   while waitTill  gt  new Date        It s blocking insofar as nothing else will happen in your script  like callbacks   But since this is a console script  maybe it is what you need

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For some people  the accepted answer is not working  I found this other answer and it is working for me  How can I pass a parameter to a setTimeout   callback   var hello    Hello World   setTimeout alert  1000  hello       hello  is the parameter being passed  you can pass all the parameters after the timeout time  Thanks to  Fabio Phms for the answer

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Best way to do this is to break your code into multiple functions  like this   function function1            stuff you want to happen right away     console log  Welcome to My Console        function function2            all the stuff you want to happen after that pause     console log  Blah blah blah blah extra-blah          call the first chunk of code right away function1        call the rest of the code and have it execute after 3 seconds setTimeout function2  3000     It s similar to JohnnyHK s solution  but much neater and easier to extend

[javascript] How can I wait In Node.js (JavaScript)? l need to pause for a period of time

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