Calculating Page Load Time In JavaScript

Question

I am trying to make a webpage that  when it starts loading  uses an Interval to start a timer   When the page fully loads  it stops the timer   but 99  of the time i get time measurements of 0 00 or 0 01 even if it takes longer   Occasionally  it says something that makes more sense like  28 or 3 10 at some times   Here is the code if it helps   var hundredthstimer   0  var secondplace   0   function addinc         hundredthstimer    1      if  inctimer    100           hundredthstimer   0          secondplace    1            var clockint   setInterval addinc  10    function init        var bconv1   document getElementById  bconverter1        var bconv2   document getElementById  bconverter2           bconv2  hide         clearInterval clockint        if  inctimer len     2           inctimer    0    inctimer            alert secondplace         inctimer     onload   init    So it basically creates a variable called hundredthstimer which is increased by  1  every 10 miliseconds  01 seconds    Then  if this number reaches 1000 1 full second   a variable called secondsplace goes up by 1  since that is how many full seconds it has run for   Then  it alerts secondsplace  a decimal point  and hundredthsplace as the total load time   But the problem above with incorrect numbers still exists  Why

User · Accepted Answer

Don t ever use the setInterval or setTimeout functions for time measuring  They are unreliable  and it is very likely that the JS execution scheduling during a documents parsing and displaying is delayed   Instead  use the Date object to create a timestamp when you page began loading  and calculate the difference to the time when the page has been fully loaded    lt doctype html gt   lt html gt       lt head gt           lt script type  text javascript  gt              var timerStart   Date now             lt  script gt           lt  -- do all the stuff you need to do -- gt       lt  head gt       lt body gt           lt  -- put everything you need in here -- gt            lt script type  text javascript  gt                 document  ready function                      console log  Time until DOMready     Date now  -timerStart                                   window  load function                      console log  Time until everything loaded     Date now  -timerStart                             lt  script gt       lt  body gt   lt  html gt

User · Answer

The answer mentioned by  HaNdTriX is a great  but we are not sure if DOM is completely loaded in the below code   var loadTime   window performance timing domContentLoadedEventEnd- window performance timing navigationStart     This works perfectly when used with onload as   window onload   function          var loadTime   window performance timing domContentLoadedEventEnd-window performance timing navigationStart       console log  Page load time is    loadTime       Edit 1  Added some context to answer   Note  loadTime  is in milliseconds  you can divide by 1000 to get seconds as mentioned by  nycynik

User · Answer

Why so complicated  When you can do   var loadTime   window performance timing domContentLoadedEventEnd- window performance timing navigationStart    If you need more times check out the window performance object   console log window performance     Will show you the timing object   connectEnd                 Time when server connection is finished  connectStart               Time just before server connection begins  domComplete                Time just before document readiness completes  domContentLoadedEventEnd   Time after DOMContentLoaded event completes  domContentLoadedEventStart Time just before DOMContentLoaded starts  domInteractive             Time just before readiness set to interactive  domLoading                 Time just before readiness set to loading  domainLookupEnd            Time after domain name lookup  domainLookupStart          Time just before domain name lookup  fetchStart                 Time when the resource starts being fetched  loadEventEnd               Time when the load event is complete  loadEventStart             Time just before the load event is fired  navigationStart            Time after the previous document begins unload  redirectCount              Number of redirects since the last non-redirect  redirectEnd                Time after last redirect response ends  redirectStart              Time of fetch that initiated a redirect  requestStart               Time just before a server request  responseEnd                Time after the end of a response or connection  responseStart              Time just before the start of a response  timing                     Reference to a performance timing object  navigation                 Reference to performance navigation object  performance                Reference to performance object for a window  type                       Type of the last non-redirect navigation event  unloadEventEnd             Time after the previous document is unloaded  unloadEventStart           Time just before the unload event is fired    Browser Support  More Info

User · Answer

It is hard to make a good timing  because the performance dominteractive is miscalulated  anyway an interesting link for timing developers    When dom is parsed it still may load and execute deferred scripts  And inline scripts waiting for css  css blocking dom  has to be loaded also until DOMContentloaded  So it is not yet parsed    And we have readystatechange event where we can look at readyState that unfortunately is missing  dom is parsed  that happens somewhere between  loaded  and  interactive     Everything becomes problematic when even not the Timing API gives us a time when dom stoped parsing HTML and starting The End process  This standard say the first point has to be that  interactive  fires precisely after dom parsed  Both Chrome and FF has implemented it when document has finished loading sometime after it has parsed  They seem to  mis interpret the standars as parsing continues beyond deferred scripts executed while people misinterpret DOMContentLoaded as something hapen before defered executing and not after  Anyway     My recommendation for you is to read about  Navigation Timing API  Or go the easy way and choose a oneliner of these  or run all three and look in your browsers console        document addEventListener  readystatechange   function     console log  Fiered      document readyState      after     performance now       ms           document addEventListener  DOMContentLoaded   function     console log  Fiered DOMContentLoaded after     performance now       ms       false      window addEventListener  load   function     console log  Fiered load after     performance now       ms       false     The time is in milliseconds after document started  I have verified with Navigation  Timing API     To get seconds for exampe from the time you did var ti   performance now   you can do parseInt performance now   - ti    1000  Instead of that kind of performance now   subtractions the code get little shorter by User Timing API where you set marks in your code and measure between marks

[javascript] Calculating Page Load Time In JavaScript

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