How to measure time taken by a function to execute

Question

I need to get execution time in milliseconds   I originally asked this question back in 2008  The accepted answer then was to use new Date   getTime   However  we can all agree now  that using the standard performance now   API is more appropriate  I am therefore changing the accepted answer to this one

User · Answer

To get precise values you should use Performance interface. It's supported in modern versions of Firefox, Chrome, Opera and IE. Here's an example of how it can be used:

var performance = window.performance;
var t0 = performance.now();
doWork();
var t1 = performance.now();
console.log("Call to doWork took " + (t1 - t0) + " milliseconds.")

Date.getTime() or console.time() are not good for measuring precise execution time. You can use them if quick rough estimate is OK for you. By rough estimate I mean you can get 15-60 ms shift from the real time.

Check this brilliant post on measuring execution time in JavaScript. The author also gives a couple of links about accuracy of JavaScript time, worth reading.

User · Answer

The best way would be to use the performance hooks module  Although unstable  you can mark specific areas of your code and measure the duration between marked areas   const   performance  PerformanceObserver     require  perf hooks     const measures       const obs   new PerformanceObserver list   gt  measures push    list getEntries      obs observe   entryTypes    measure       const getEntriesByType   cb   gt  cb measures    const doSomething   val   gt      performance mark  beginning of the process       val    2     performance mark  after multiplication       performance measure  time taken    beginning of the process    after multiplication       getEntriesByType entries   gt        entries forEach entry   gt  console log entry            return val     doSomething 4     Try here

User · Answer

A couple months ago I put together my own routine that times a function using Date now   -- even though at the time the accepted method seemed to be performance now   --  because the performance object is not yet available  built-in  in the stable Node js release   Today I was doing some more research and found another method for timing  Since I also found how to use this in Node js code  I thought I would share it here    The following is combined from the examples given by w3c and Node js   function functionTimer         performance mark  start       functionToBeTimed       performance mark  end       performance measure  Start to End    start    end       const measure   performance getEntriesByName  Start to End   0      console log measure duration      NOTE   If you intend to use the performance object in a Node js app  you must include the following require    const   performance     require  perf hooks

User · Answer

Thanks  Achim Koellner  will expand your answer a bit   var t0   process hrtime      Start of code to measure    End of code var timeInMilliseconds   process hrtime t0  1  1000000     dividing by 1000000 gives milliseconds from nanoseconds   Please  note  that you shouldn t do anything apart from what you want to measure  for example  console log will also take time to execute and will affect performance tests    Note  that in order by measure asynchronous functions execution time  you should insert var timeInMilliseconds   process hrtime t0  1  1000000  inside the callback  For example   var t0   process hrtime    someAsyncFunction function err  results    var timeInMilliseconds   process hrtime t0  1  1000000

User · Answer

If you need to get function execution time on your local development machine  you can either use your browser s profiling tools  or console commands such as console time   and console timeEnd     All modern browsers have JavaScript profilers built-in   These profilers should give the most accurate measurement as you do not have to modify your existing code  which could affect the function s execution time   To profile your JavaScript    In Chrome  press F12 and select the Profiles tab  then Collect JavaScript CPU Profile  In Firefox  install open Firebug  and click on the Profile button    In IE 9   press F12  click on Script or Profiler  depending on your version of IE     Alternatively  on your development machine  you can add instrumentation to your code with console time   and console timeEnd     These functions  supported in Firefox11   Chrome2  and IE11   report on timers that you start stop via console time     time   takes a user-defined timer name as an argument  and timeEnd   then reports on the execution time since the timer started   function a       console time  mytimer          do stuff       var dur   console timeEnd  myTimer       NOTE  dur only works in FF     Note that only Firefox returns the elapsed time in the timeEnd   call   The other browsers simply report the result to the developer console  the return value of timeEnd   is undefined   If you want to get function execution time in the wild  you will have to instrument your code   You have a couple options   You can simply save the start and end times by querying new Date   getTime     function a       var start   new Date   getTime          do stuff       var end   new Date   getTime      var dur   end - start      However  the Date object only has millisecond resolution and will be affected by any OS s system clock changes   In modern browsers  there s a better option   The better option is to use the High Resolution Time  aka window performance now     now   is better than the traditional Date getTime   in two important ways    now   is a double with submillisecond resolution that represents the number of milliseconds since the start of the page s navigation   It returns the number of microseconds in the fractional  e g  a value of 1000 123 is 1 second and 123 microseconds   now   is monotonically increasing   This is important as Date getTime   can possibly jump forward or even backward on subsequent calls   Notably  if the OS s system time is updated  e g  atomic clock synchronization   Date getTime   is also updated   now   is guaranteed to always be monotonically increasing  so it is not affected by the OS s system time -- it will always be wall-clock time  assuming your wall clock is not atomic        now   can be used in almost every place that new Date   getTime      new Date andt Date now   are   The exception is that Date and now   times don t mix  as Date is based on unix-epoch  the number of milliseconds since 1970   while now   is the number of milliseconds since your page navigation started  so it will be much smaller than Date    Here s an example of how to use now     function a       var start   window performance now           do stuff       var end   window performance now      var dur   end - start      now   is supported in Chrome stable  Firefox 15   and IE10   There are also several polyfills available   One other option for measuring execution time in the wild is UserTiming   UserTiming behaves similarly to console time   and console timeEnd    but it utilizes the same High Resolution Timestamp that now   uses  so you get a sub-millisecond monotonically increasing clock   and saves the timestamps and durations to the PerformanceTimeline   UserTiming has the concepts of marks  timestamps  and measures  durations    You can define as many of either as you want  and they re exposed on the PerformanceTimeline   To save a timestamp  you call mark startMarkName    To get the duration since your first mark  you simply call measure measurename  startMarkname    The duration is then saved in the PerformanceTimeline alongside your marks   function a       window performance mark  start          do stuff       window performance measure  myfunctionduration    start          duration is window performance getEntriesByName  myfunctionduration    measure   0     UserTiming is available in IE10  and Chrome25    There is also a polyfill available  which I wrote

User · Answer

there are multiple ways to achieve this objective      using console time   console time  function      run the function in between these two lines for that you need to    measure time taken by the function    ex  function      console timeEnd  function     this  is the most efficient way   using performance now    e g    var v1   performance now      run the function here for which you have top measure the time  var v2   performance now    console log  total time  taken      v2-v1   milliseconds     use   add operator  or getTime    var h2    new Date      or var h2   new Date   getTime    for i 0 i lt 500 i         do something     var h3    new Date        or  var h3   new Date   getTime    var timeTaken   h3-h2  console log  time        timeTaken      Here s what happens when you apply the unary plus operator to a Date instance           Get the value of the Date instance in question          Convert it to a Number  NOTE  getTime   gives better performance than unary   operator

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Use Firebug  enable both Console and Javascript   Click Profile   Reload   Click Profile again   View the report

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var StopWatch   function  performance        this startTime   0      this stopTime   0      this running   false      this performance   performance     false   false     window performance      StopWatch prototype currentTime   function          return this performance   window performance now     new Date   getTime        StopWatch prototype start   function          this startTime   this currentTime        this running   true      StopWatch prototype stop   function          this stopTime   this currentTime        this running   false      StopWatch prototype getElapsedMilliseconds   function          if  this running            this stopTime   this currentTime               return this stopTime - this startTime      StopWatch prototype getElapsedSeconds   function          return this getElapsedMilliseconds     1000      StopWatch prototype printElapsed   function  name        var currentName   name     Elapsed         console log currentName        this getElapsedMilliseconds      ms          this getElapsedSeconds      s          Benchmark  var stopwatch   new StopWatch    stopwatch start     for  var index   0  index  lt  100  index          stopwatch printElapsed  Instance     index            stopwatch stop     stopwatch printElapsed      Output  Instance 0   0ms   0s  Instance 1   2 999999967869371ms   0 002999999967869371s  Instance 2   2 999999967869371ms   0 002999999967869371s            Instance 99   10 999999998603016ms   0 010999999998603016s  Elapsed   10 999999998603016ms   0 010999999998603016s    performance now   is optional - just pass false into StopWatch constructor function

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To extend vsync s code further to have the ability to return the timeEnd as a value in NodeJS use this little piece of code   console timeEndValue   function label       Add console timeEndValue  to add a return value    var time   this  times label      if   time         throw new Error  No such label      label           var duration   Date now   - time     return duration       Now use the code like so   console time  someFunction timer     someFunction     var executionTime   console timeEndValue  someFunction timer    console log  The execution time is     executionTime     This gives you more possibilities  You can store the execution time to be used for more purposes like using it in equations  or stored in a database  sent to a remote client over websockets  served on a webpage  etc

User · Answer

Don t use Date    Read below   Use performance now      lt script gt  var a   performance now    alert  do something       var b   performance now    alert  It took      b - a      ms      lt  script gt    It works on     IE 10    FireFox 15    Chrome 24    Safari 8    Opera 15     Android 4 4    etc  etc   console time may be viable for you  but it s non-standard  sect       This feature is non-standard and is not on a standards track  Do not use it on production sites facing the Web  it will not work for every user  There may also be large incompatibilities between implementations and the behavior may change in the future    Besides browser support  performance now seems to have the potential to provide more accurate timings as it appears to be the bare-bones version of console time      lt rant  Also  DON T EVER use Date for anything because  it s affected by changes in  system time   Which means we will get invalid results  mdash like  negative timing  mdash  when the user doesn t have an accurate system time      On Oct 2014  my system clock went haywire and guess what     I opened Gmail and saw all of my day s emails  sent 0 minutes ago   And I d thought Gmail is supposed to be built by world-class engineers from Google           Set your system clock to one year ago and go to Gmail so we can all have a good laugh  Perhaps someday we will have a Hall of Shame for JS Date    Google Spreadsheet s now   function also suffers from this problem   The only time you ll be using Date is when you want to show the user his system clock time  Not when you want to get the time or to measure anything

User · Answer

there are multiple ways to achieve this objective      using console time   console time  function      run the function in between these two lines for that you need to    measure time taken by the function    ex  function      console timeEnd  function     this  is the most efficient way   using performance now    e g    var v1   performance now      run the function here for which you have top measure the time  var v2   performance now    console log  total time  taken      v2-v1   milliseconds     use   add operator  or getTime    var h2    new Date      or var h2   new Date   getTime    for i 0 i lt 500 i         do something     var h3    new Date        or  var h3   new Date   getTime    var timeTaken   h3-h2  console log  time        timeTaken      Here s what happens when you apply the unary plus operator to a Date instance           Get the value of the Date instance in question          Convert it to a Number  NOTE  getTime   gives better performance than unary   operator

User · Answer

use new Date   getTime       The getTime   method returns the number of milliseconds since midnight of January 1  1970    ex   var start   new Date   getTime     for  i   0  i  lt  50000    i       do something    var end   new Date   getTime    var time   end - start  alert  Execution time      time

User · Answer

As previously stated check for and use built in timer  But if you want or need to write your own here is my two cents      -  Source  -           JavaScript Timer Object            var now timer  elapsed               timer  stop              timer  start              timer  reset              expose     method timer     return  number      timer function        var a Date now        b 0      return               expose            elapsed function   return b Date now  -a           start function   return a Date now             stop function   return Date now             reset function   return a 0                 -  Google Advanced Optimized  -    timer function   var a Date now   b 0 return a function   return b Date now  -a  start function   return a Date now    stop function   return Date now    reset function   return a 0         Compilation was a success    Original Size     219 bytes gzipped  405 bytes uncompressed  Compiled Size     109 bytes gzipped  187 bytes uncompressed  Saved 50 23  off the gzipped size  53 83  without gzip

User · Answer

Here s a decorator for timing functions  let timed    f    gt      args   gt       let start   performance now        let ret   f    args       console log  function   f name  took    performance now  -start  toFixed 3  ms       return ret         Usage   let test       gt    does something    test   timed test       turns the function into a timed function in one line test                    run your code as normal  logs  function test took 1001 900ms     If you re using async functions you can make timed async and add an await before f    args   and that should work for those  It gets more complicated if you want one decorator to handle both sync and async functions

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export default class Singleton      static myInstance  Singleton   null      timers  any                    returns  Singleton          static getInstance         if  Singleton myInstance    null          Singleton myInstance   new Singleton               return this myInstance         initTime label  string        this  timers label    Date now        return this  timers label          endTime label  string        const endTime   Date now        if  this  timers label           const delta   endTime - this  timers label         const finalTime      label     delta ms         delete this  timers label         return finalTime        else         return null                InitTime related to string   return Singleton getInstance   initTime label      Returns the time init  return Singleton getInstance   endTime label      Returns the total time between init and end

User · Answer

If you need to get function execution time on your local development machine  you can either use your browser s profiling tools  or console commands such as console time   and console timeEnd     All modern browsers have JavaScript profilers built-in   These profilers should give the most accurate measurement as you do not have to modify your existing code  which could affect the function s execution time   To profile your JavaScript    In Chrome  press F12 and select the Profiles tab  then Collect JavaScript CPU Profile  In Firefox  install open Firebug  and click on the Profile button    In IE 9   press F12  click on Script or Profiler  depending on your version of IE     Alternatively  on your development machine  you can add instrumentation to your code with console time   and console timeEnd     These functions  supported in Firefox11   Chrome2  and IE11   report on timers that you start stop via console time     time   takes a user-defined timer name as an argument  and timeEnd   then reports on the execution time since the timer started   function a       console time  mytimer          do stuff       var dur   console timeEnd  myTimer       NOTE  dur only works in FF     Note that only Firefox returns the elapsed time in the timeEnd   call   The other browsers simply report the result to the developer console  the return value of timeEnd   is undefined   If you want to get function execution time in the wild  you will have to instrument your code   You have a couple options   You can simply save the start and end times by querying new Date   getTime     function a       var start   new Date   getTime          do stuff       var end   new Date   getTime      var dur   end - start      However  the Date object only has millisecond resolution and will be affected by any OS s system clock changes   In modern browsers  there s a better option   The better option is to use the High Resolution Time  aka window performance now     now   is better than the traditional Date getTime   in two important ways    now   is a double with submillisecond resolution that represents the number of milliseconds since the start of the page s navigation   It returns the number of microseconds in the fractional  e g  a value of 1000 123 is 1 second and 123 microseconds   now   is monotonically increasing   This is important as Date getTime   can possibly jump forward or even backward on subsequent calls   Notably  if the OS s system time is updated  e g  atomic clock synchronization   Date getTime   is also updated   now   is guaranteed to always be monotonically increasing  so it is not affected by the OS s system time -- it will always be wall-clock time  assuming your wall clock is not atomic        now   can be used in almost every place that new Date   getTime      new Date andt Date now   are   The exception is that Date and now   times don t mix  as Date is based on unix-epoch  the number of milliseconds since 1970   while now   is the number of milliseconds since your page navigation started  so it will be much smaller than Date    Here s an example of how to use now     function a       var start   window performance now           do stuff       var end   window performance now      var dur   end - start      now   is supported in Chrome stable  Firefox 15   and IE10   There are also several polyfills available   One other option for measuring execution time in the wild is UserTiming   UserTiming behaves similarly to console time   and console timeEnd    but it utilizes the same High Resolution Timestamp that now   uses  so you get a sub-millisecond monotonically increasing clock   and saves the timestamps and durations to the PerformanceTimeline   UserTiming has the concepts of marks  timestamps  and measures  durations    You can define as many of either as you want  and they re exposed on the PerformanceTimeline   To save a timestamp  you call mark startMarkName    To get the duration since your first mark  you simply call measure measurename  startMarkname    The duration is then saved in the PerformanceTimeline alongside your marks   function a       window performance mark  start          do stuff       window performance measure  myfunctionduration    start          duration is window performance getEntriesByName  myfunctionduration    measure   0     UserTiming is available in IE10  and Chrome25    There is also a polyfill available  which I wrote

User · Answer

Thanks  Achim Koellner  will expand your answer a bit   var t0   process hrtime      Start of code to measure    End of code var timeInMilliseconds   process hrtime t0  1  1000000     dividing by 1000000 gives milliseconds from nanoseconds   Please  note  that you shouldn t do anything apart from what you want to measure  for example  console log will also take time to execute and will affect performance tests    Note  that in order by measure asynchronous functions execution time  you should insert var timeInMilliseconds   process hrtime t0  1  1000000  inside the callback  For example   var t0   process hrtime    someAsyncFunction function err  results    var timeInMilliseconds   process hrtime t0  1  1000000

User · Answer

To start the timer use console time  myTimer     Optional  To print the elapsed time  use console timeLog  myTimer    Finally  to stop the timer and print the final time  console timeEnd  myTimer      You can read more about this on MDN and in the Node js documentation   Available on Chrome  Firefox  Opera and NodeJS   not on Edge or Internet Explorer

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Use Firebug  enable both Console and Javascript   Click Profile   Reload   Click Profile again   View the report

User · Answer

use new Date   getTime       The getTime   method returns the number of milliseconds since midnight of January 1  1970    ex   var start   new Date   getTime     for  i   0  i  lt  50000    i       do something    var end   new Date   getTime    var time   end - start  alert  Execution time      time

User · Answer

It may help you   var t0   date now    doSomething    var t1   date now    console log  Call to doSomething took approximate     t1 - t0  1000     seconds

User · Answer

you can use add operator also here   var start    new Date     callYourFunctionHere     var end    new Date     var time   end - start   console log  total execution time      time    ms

User · Answer

use new Date   getTime       The getTime   method returns the number of milliseconds since midnight of January 1  1970    ex   var start   new Date   getTime     for  i   0  i  lt  50000    i       do something    var end   new Date   getTime    var time   end - start  alert  Execution time      time

User · Answer

The best way would be to use the performance hooks module  Although unstable  you can mark specific areas of your code and measure the duration between marked areas   const   performance  PerformanceObserver     require  perf hooks     const measures       const obs   new PerformanceObserver list   gt  measures push    list getEntries      obs observe   entryTypes    measure       const getEntriesByType   cb   gt  cb measures    const doSomething   val   gt      performance mark  beginning of the process       val    2     performance mark  after multiplication       performance measure  time taken    beginning of the process    after multiplication       getEntriesByType entries   gt        entries forEach entry   gt  console log entry            return val     doSomething 4     Try here

User · Answer

The accepted answer is wrong     Since JavaScript is asynchronous  the values of the variable end of the accepted answer would be wrong   var start   new Date   getTime     for  i   0  i  lt  50000    i       JavaScript is not waiting until the for is finished       var end   new Date   getTime    var time   end - start  alert  Execution time      time      The execution of the for may be very fast so you can not see that the result is wrong  You can test it with a code doing some request    var start   new Date   getTime     for  i   0  i  lt  50000    i        ajax       url   www oneOfYourWebsites com       success  function           console log  success                   var end   new Date   getTime    var time   end - start  alert  Execution time      time      So the alert will prompt very quickly but in the console you ll see that the ajax requests are continuing    Here is how you should do it   https   developer mozilla org en-US docs Web API Performance now

User · Answer

It is possible to use only one variable   var timer   -performance now        Do something  timer    performance now    console log  Time       timer 1000  toFixed 5      sec      timer 1000 - to convert milliseconds to seconds   toFixed 5  - to trim extra digits

User · Answer

A couple months ago I put together my own routine that times a function using Date now   -- even though at the time the accepted method seemed to be performance now   --  because the performance object is not yet available  built-in  in the stable Node js release   Today I was doing some more research and found another method for timing  Since I also found how to use this in Node js code  I thought I would share it here    The following is combined from the examples given by w3c and Node js   function functionTimer         performance mark  start       functionToBeTimed       performance mark  end       performance measure  Start to End    start    end       const measure   performance getEntriesByName  Start to End   0      console log measure duration      NOTE   If you intend to use the performance object in a Node js app  you must include the following require    const   performance     require  perf hooks

User · Answer

As previously stated check for and use built in timer  But if you want or need to write your own here is my two cents      -  Source  -           JavaScript Timer Object            var now timer  elapsed               timer  stop              timer  start              timer  reset              expose     method timer     return  number      timer function        var a Date now        b 0      return               expose            elapsed function   return b Date now  -a           start function   return a Date now             stop function   return Date now             reset function   return a 0                 -  Google Advanced Optimized  -    timer function   var a Date now   b 0 return a function   return b Date now  -a  start function   return a Date now    stop function   return Date now    reset function   return a 0         Compilation was a success    Original Size     219 bytes gzipped  405 bytes uncompressed  Compiled Size     109 bytes gzipped  187 bytes uncompressed  Saved 50 23  off the gzipped size  53 83  without gzip

User · Answer

var StopWatch   function  performance        this startTime   0      this stopTime   0      this running   false      this performance   performance     false   false     window performance      StopWatch prototype currentTime   function          return this performance   window performance now     new Date   getTime        StopWatch prototype start   function          this startTime   this currentTime        this running   true      StopWatch prototype stop   function          this stopTime   this currentTime        this running   false      StopWatch prototype getElapsedMilliseconds   function          if  this running            this stopTime   this currentTime               return this stopTime - this startTime      StopWatch prototype getElapsedSeconds   function          return this getElapsedMilliseconds     1000      StopWatch prototype printElapsed   function  name        var currentName   name     Elapsed         console log currentName        this getElapsedMilliseconds      ms          this getElapsedSeconds      s          Benchmark  var stopwatch   new StopWatch    stopwatch start     for  var index   0  index  lt  100  index          stopwatch printElapsed  Instance     index            stopwatch stop     stopwatch printElapsed      Output  Instance 0   0ms   0s  Instance 1   2 999999967869371ms   0 002999999967869371s  Instance 2   2 999999967869371ms   0 002999999967869371s            Instance 99   10 999999998603016ms   0 010999999998603016s  Elapsed   10 999999998603016ms   0 010999999998603016s    performance now   is optional - just pass false into StopWatch constructor function

User · Answer

process hrtime   is available within Node js - it returns a value in nanoseconds  var hrTime   process hrtime   console log hrTime 0    1000000   hrTime 1    1000

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In my case  I perfer to use   grammar suger and compile it with babel  The problem of this method is that function has to be inside object     Sample JS Code  function timer         return  target  propertyKey  descriptor    gt            const start   Date now            let oldFunc   descriptor value           descriptor value   async function                 var result   await oldFunc apply this  arguments               console log Date now   - start               return result                        Util function  function delay timeout        return new Promise  resolve    gt  setTimeout      gt            resolve           timeout       class Test        timer       async test timout            await delay timout          console log  delay 1            await delay timout          console log  delay 2             const t   new Test    t test 1000  t test 100     babelrc  for babel 6           plugins              transform-decorators-legacy

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It may help you   var t0   date now    doSomething    var t1   date now    console log  Call to doSomething took approximate     t1 - t0  1000     seconds

User · Answer

Stopwatch with cumulative cycles  Works with server and client  Node or DOM   uses the Performance API   Good when you have many small cycles e g  in a function called 1000 times that processes 1000 data objects but you want to see how each operation in this function adds up to the total   So this one uses a module global  singleton  timer  Same as a class singleton pattern  just a bit simpler to use  but you need to put this in a separate e g  stopwatch js file   const perf   typeof performance      undefined    performance   require  perf hooks   performance  const DIGITS   2   let  timers        const  log    label  delta     gt        if   timers label             console log    label        delta      delta toFixed DIGITS   ms last                            timers label  total toFixed DIGITS   ms total     timers label  cycles  cycles              export const Stopwatch         start label            const now   perf now            if   timers label                 if    timers label  started                     timers label  started   now                          else                timers label                      started  now                  total  0                  cycles  0                                         Returns total elapsed milliseconds  or null if stopwatch doesn t exist         stop label  log   false            const now   perf now            if   timers label                 let delta              if  timers label  started                    delta   now -  timers label  started                   timers label  started   null                   timers label  total    delta                   timers label  cycles                              log  amp  amp   log label  delta               return  timers label  total            else               return null                           Logs total time        log   log      delete label            delete  timers label

User · Answer

process hrtime   is available within Node js - it returns a value in nanoseconds  var hrTime   process hrtime   console log hrTime 0    1000000   hrTime 1    1000

User · Answer

With performance  NodeJs  It is required to import the performance class  var time0   performance now       Store the time at this point into time0  yourFunction         The function you re measuring time for   var time1   performance now       Store the time at this point into time1  console log  youFunction took      time1 - time0      milliseconds to execute      Using console time  console time  someFunction     someFunction       Whatever is timed goes between the two  console time   console timeEnd  someFunction

User · Answer

With performance  NodeJs  It is required to import the performance class  var time0   performance now       Store the time at this point into time0  yourFunction         The function you re measuring time for   var time1   performance now       Store the time at this point into time1  console log  youFunction took      time1 - time0      milliseconds to execute      Using console time  console time  someFunction     someFunction       Whatever is timed goes between the two  console time   console timeEnd  someFunction

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Since console time and performance now aren t supported in some major browsers  i e  IE10   I created a slim utility that utilizes the best available methods  However  it lacks error handling for false usages  calling End   on a not initialized timer    Use it and improve it as you want    Performance        Timer          Start  function  name            if  console  amp  amp  console time                console time name             else if  window performance now                this Timer name    window performance now              else               this Timer name    new Date   getTime                         End  function  name            if  console  amp  amp  console time                console timeEnd name             else               var result              if  window performance now                    result   window performance now   - this Timer name                 else                   result   new Date   getTime   - this Timer name                             console log name          result

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Don t use Date    Read below   Use performance now      lt script gt  var a   performance now    alert  do something       var b   performance now    alert  It took      b - a      ms      lt  script gt    It works on     IE 10    FireFox 15    Chrome 24    Safari 8    Opera 15     Android 4 4    etc  etc   console time may be viable for you  but it s non-standard  sect       This feature is non-standard and is not on a standards track  Do not use it on production sites facing the Web  it will not work for every user  There may also be large incompatibilities between implementations and the behavior may change in the future    Besides browser support  performance now seems to have the potential to provide more accurate timings as it appears to be the bare-bones version of console time      lt rant  Also  DON T EVER use Date for anything because  it s affected by changes in  system time   Which means we will get invalid results  mdash like  negative timing  mdash  when the user doesn t have an accurate system time      On Oct 2014  my system clock went haywire and guess what     I opened Gmail and saw all of my day s emails  sent 0 minutes ago   And I d thought Gmail is supposed to be built by world-class engineers from Google           Set your system clock to one year ago and go to Gmail so we can all have a good laugh  Perhaps someday we will have a Hall of Shame for JS Date    Google Spreadsheet s now   function also suffers from this problem   The only time you ll be using Date is when you want to show the user his system clock time  Not when you want to get the time or to measure anything

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If you want to measure the time between multiple things that aren t nested you could use this   function timer lap        if lap  console log    lap  in     performance now  -timer prev  toFixed 3  ms         timer prev   performance now        Similar to console time    but easier usage if you don t need to keep track of previous timers   If you like the blue color from console time    you can use this line instead  console log    lap  in   c   performance now  -timer prev  toFixed 3  ms    color blue           Usage   timer                   set the start    do something  timer  built            logs  built in  591 815ms     do something timer  copied           logs  copied in  0 065ms     do something timer  compared         logs  compared in  36 41ms

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To get precise values you should use Performance interface. It's supported in modern versions of Firefox, Chrome, Opera and IE. Here's an example of how it can be used:

var performance = window.performance;
var t0 = performance.now();
doWork();
var t1 = performance.now();
console.log("Call to doWork took " + (t1 - t0) + " milliseconds.")

Date.getTime() or console.time() are not good for measuring precise execution time. You can use them if quick rough estimate is OK for you. By rough estimate I mean you can get 15-60 ms shift from the real time.

Check this brilliant post on measuring execution time in JavaScript. The author also gives a couple of links about accuracy of JavaScript time, worth reading.

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Use Firebug  enable both Console and Javascript   Click Profile   Reload   Click Profile again   View the report

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Stopwatch with cumulative cycles  Works with server and client  Node or DOM   uses the Performance API   Good when you have many small cycles e g  in a function called 1000 times that processes 1000 data objects but you want to see how each operation in this function adds up to the total   So this one uses a module global  singleton  timer  Same as a class singleton pattern  just a bit simpler to use  but you need to put this in a separate e g  stopwatch js file   const perf   typeof performance      undefined    performance   require  perf hooks   performance  const DIGITS   2   let  timers        const  log    label  delta     gt        if   timers label             console log    label        delta      delta toFixed DIGITS   ms last                            timers label  total toFixed DIGITS   ms total     timers label  cycles  cycles              export const Stopwatch         start label            const now   perf now            if   timers label                 if    timers label  started                     timers label  started   now                          else                timers label                      started  now                  total  0                  cycles  0                                         Returns total elapsed milliseconds  or null if stopwatch doesn t exist         stop label  log   false            const now   perf now            if   timers label                 let delta              if  timers label  started                    delta   now -  timers label  started                   timers label  started   null                   timers label  total    delta                   timers label  cycles                              log  amp  amp   log label  delta               return  timers label  total            else               return null                           Logs total time        log   log      delete label            delete  timers label

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Since console time and performance now aren t supported in some major browsers  i e  IE10   I created a slim utility that utilizes the best available methods  However  it lacks error handling for false usages  calling End   on a not initialized timer    Use it and improve it as you want    Performance        Timer          Start  function  name            if  console  amp  amp  console time                console time name             else if  window performance now                this Timer name    window performance now              else               this Timer name    new Date   getTime                         End  function  name            if  console  amp  amp  console time                console timeEnd name             else               var result              if  window performance now                    result   window performance now   - this Timer name                 else                   result   new Date   getTime   - this Timer name                             console log name          result

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The accepted answer is wrong     Since JavaScript is asynchronous  the values of the variable end of the accepted answer would be wrong   var start   new Date   getTime     for  i   0  i  lt  50000    i       JavaScript is not waiting until the for is finished       var end   new Date   getTime    var time   end - start  alert  Execution time      time      The execution of the for may be very fast so you can not see that the result is wrong  You can test it with a code doing some request    var start   new Date   getTime     for  i   0  i  lt  50000    i        ajax       url   www oneOfYourWebsites com       success  function           console log  success                   var end   new Date   getTime    var time   end - start  alert  Execution time      time      So the alert will prompt very quickly but in the console you ll see that the ajax requests are continuing    Here is how you should do it   https   developer mozilla org en-US docs Web API Performance now

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To start the timer use console time  myTimer     Optional  To print the elapsed time  use console timeLog  myTimer    Finally  to stop the timer and print the final time  console timeEnd  myTimer      You can read more about this on MDN and in the Node js documentation   Available on Chrome  Firefox  Opera and NodeJS   not on Edge or Internet Explorer

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To extend vsync s code further to have the ability to return the timeEnd as a value in NodeJS use this little piece of code   console timeEndValue   function label       Add console timeEndValue  to add a return value    var time   this  times label      if   time         throw new Error  No such label      label           var duration   Date now   - time     return duration       Now use the code like so   console time  someFunction timer     someFunction     var executionTime   console timeEndValue  someFunction timer    console log  The execution time is     executionTime     This gives you more possibilities  You can store the execution time to be used for more purposes like using it in equations  or stored in a database  sent to a remote client over websockets  served on a webpage  etc

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It is possible to use only one variable   var timer   -performance now        Do something  timer    performance now    console log  Time       timer 1000  toFixed 5      sec      timer 1000 - to convert milliseconds to seconds   toFixed 5  - to trim extra digits

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export default class Singleton      static myInstance  Singleton   null      timers  any                    returns  Singleton          static getInstance         if  Singleton myInstance    null          Singleton myInstance   new Singleton               return this myInstance         initTime label  string        this  timers label    Date now        return this  timers label          endTime label  string        const endTime   Date now        if  this  timers label           const delta   endTime - this  timers label         const finalTime      label     delta ms         delete this  timers label         return finalTime        else         return null                InitTime related to string   return Singleton getInstance   initTime label      Returns the time init  return Singleton getInstance   endTime label      Returns the total time between init and end

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Using  performance now     var t0   performance now    doSomething         lt ---- The function you re measuring time for   var t1   performance now   console log  Call to doSomething took      t1 - t0      milliseconds         NodeJs  it is required to import the performance class     Using console time   non-standard   living standard   console time  someFunction    someFunction      Whatever is timed goes between the two  console time   console timeEnd  someFunction     Note  The string being pass to the time   and timeEnd   methods must match for the timer to finish as expected       console time   documentations          NodeJS documentation regarding   MDN  client-side  documentation

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Here s a decorator for timing functions  let timed    f    gt      args   gt       let start   performance now        let ret   f    args       console log  function   f name  took    performance now  -start  toFixed 3  ms       return ret         Usage   let test       gt    does something    test   timed test       turns the function into a timed function in one line test                    run your code as normal  logs  function test took 1001 900ms     If you re using async functions you can make timed async and add an await before f    args   and that should work for those  It gets more complicated if you want one decorator to handle both sync and async functions

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Using  performance now     var t0   performance now    doSomething         lt ---- The function you re measuring time for   var t1   performance now   console log  Call to doSomething took      t1 - t0      milliseconds         NodeJs  it is required to import the performance class     Using console time   non-standard   living standard   console time  someFunction    someFunction      Whatever is timed goes between the two  console time   console timeEnd  someFunction     Note  The string being pass to the time   and timeEnd   methods must match for the timer to finish as expected       console time   documentations          NodeJS documentation regarding   MDN  client-side  documentation

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use new Date   getTime       The getTime   method returns the number of milliseconds since midnight of January 1  1970    ex   var start   new Date   getTime     for  i   0  i  lt  50000    i       do something    var end   new Date   getTime    var time   end - start  alert  Execution time      time

User · Answer

If you want to measure the time between multiple things that aren t nested you could use this   function timer lap        if lap  console log    lap  in     performance now  -timer prev  toFixed 3  ms         timer prev   performance now        Similar to console time    but easier usage if you don t need to keep track of previous timers   If you like the blue color from console time    you can use this line instead  console log    lap  in   c   performance now  -timer prev  toFixed 3  ms    color blue           Usage   timer                   set the start    do something  timer  built            logs  built in  591 815ms     do something timer  copied           logs  copied in  0 065ms     do something timer  compared         logs  compared in  36 41ms

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Use Firebug  enable both Console and Javascript   Click Profile   Reload   Click Profile again   View the report

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you can use add operator also here   var start    new Date     callYourFunctionHere     var end    new Date     var time   end - start   console log  total execution time      time    ms

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In my case  I perfer to use   grammar suger and compile it with babel  The problem of this method is that function has to be inside object     Sample JS Code  function timer         return  target  propertyKey  descriptor    gt            const start   Date now            let oldFunc   descriptor value           descriptor value   async function                 var result   await oldFunc apply this  arguments               console log Date now   - start               return result                        Util function  function delay timeout        return new Promise  resolve    gt  setTimeout      gt            resolve           timeout       class Test        timer       async test timout            await delay timout          console log  delay 1            await delay timout          console log  delay 2             const t   new Test    t test 1000  t test 100     babelrc  for babel 6           plugins              transform-decorators-legacy

[javascript] How to measure time taken by a function to execute

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