Adding hours to JavaScript Date object

Question

It amazes me that JavaScript s Date object does not implement an add function of any kind   I simply want a function that can do this   var now   Date now    var fourHoursLater   now addHours 4    function Date prototype addHours h           how do I implement this         I would simply like some pointers in a direction    Do I need to do string parsing    Can I use setTime  How about milliseconds    Like this   new Date milliseconds   4 3600 1000   4 hrs in ms         This seems really hackish though - and does it even work

User · Answer

This is a easy way to get incremented or decremented data value   const date   new Date   const inc   1000   60   60    an hour const dec    1000   60   60    -1    an hour  const  date   new Date date  return new Date   date getTime     inc   return new Date   date getTime     dec

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Date prototype addHours  function h       this setHours this getHours   h       return this      Test   alert new Date   addHours 4

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You can use the momentjs http   momentjs com  Library   var moment   require  moment    foo   new moment something  add 10   m   toDate

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It is probably better to make the addHours method immutable by returning a copy of the Date object rather than mutating its parameter   Date prototype addHours  function h       var copiedDate   new Date this getTime         copiedDate setHours copiedDate getHours   h       return copiedDate      This way you can chain a bunch of method calls without worrying about state

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SPRBRN is correct  In order to account for the beginning end of the month and year  you need to convert to Epoch and back  Here s how you do that   var milliseconds   0             amount of time from current date time var sec   0                           future var min   0                       -   past var hours   2  var days   0   var startDate   new Date          start date in local time  we ll use current time as an example   var time   startDate getTime      convert to milliseconds since epoch    add time difference var newTime   time   milliseconds    1000 sec     1000 60 min     1000 60 60 hrs     1000 60 60 24 days    var newDate   new Date newTime     convert back to date  in this example  2 hours from right now   or do it in one line  where variable names are the same as above  var newDate        new Date startDate getTime     millisecond            1000    sec   60    min   60    hours   24   days

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The below code is to add 4 hours to date example today s date   var today   new Date    today setHours today getHours     4     It will not cause error if you try to add 4 to 23  see the docs       If a parameter you specify is outside of the expected range  setHours   attempts to update the date information in the Date object accordingly

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There is an add in the Datejs library   And here are the JavaScript date methods  kennebec wisely mentioned getHours   and setHours

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JavaScript itself has terrible Date Time API s  Nonetheless  you can do this in pure JavaScript   Date prototype addHours   function h      this setTime this getTime      h 60 60 1000      return this

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Check if its not already defined  otherwise defines it on the Date prototype   if   Date prototype addHours        Date prototype addHours   function h            this setHours this getHours     h           return this

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If someone is still looking at this issue  the easiest way to do is var d   new Date    d   new Date d setHours d getHours     2     it will add 2 hours in current time  Value of d   Sat Jan 30 2021 23 41 43 GMT 0500  Pakistan Standard Time  Value of d after adding 2 hours   Sun Jan 31 2021 01 41 43 GMT 0500  Pakistan Standard Time

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Another way to handle this is to convert the date to unixtime  epoch   then add the equivalent in  milli seconds  then convert it back  This way you can handle day and month transitions  like adding 4 hours to 21  which should result in the next day  01 00

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A little messy  but it works    Given a date format like this  2019-04-03T15 58      Get the start date    var start       start date   val        Split the date and time    var startarray   start split  T      var date   startarray 0     var time   startarray 1        Split the hours and minutes    var timearray   time split          var hour   timearray 0     var minute   timearray 1       Add an hour to the hour    hour            end date   val   start        end date   val    date  T  hour     minute        Your output would be   2019-04-03T16 58

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I also think the original object should not be modified  So to save future manpower here s a combined solution based on Jason Harwig s and Tahir Hasan answers   Date prototype addHours  function h       var copiedDate   new Date        copiedDate setTime this getTime      h 60 60 1000         return copiedDate

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The version suggested by kennebec will fail when changing to or from DST  since it is the hour number that is set    this setUTCHours this getUTCHours   h     will add h hours to this independent of time system peculiarities  Jason Harwig s method works as well

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If you would like to do it in a more functional way  immutability  I would return a new date object instead of modifying the existing and I wouldn t alter the prototype but create a standalone function  Here is the example   x000D   x000D    JS function addHoursToDate date  hours      return new Date new Date date  setHours date getHours     hours         TS function addHoursToDate date  Date  hours  number   Date     return new Date new Date date  setHours date getHours     hours       let myDate   new Date     console log myDate  console log addHoursToDate myDate 2   x000D   x000D   x000D

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For a simple add subtract hour minute function in javascript  try this   function getTime  addHour  addMin       addHour    addHour addHour 0       addMin    addMin addMin 0       var time   new Date new Date   getTime         var AM   true      var ndble   0      var hours  newHour  overHour  newMin  overMin        change form 24 to 12 hour clock     if time getHours    gt   13           hours   time getHours   - 12          AM    hours gt  12 true false        else          hours   time getHours            AM    hours gt  12 false true               get the current minutes     var minutes   time getMinutes           set minute     if  minutes addMin   gt   60     minutes addMin  lt 0           overMin    minutes addMin  60          overHour   Math floor  minutes addMin-Math abs overMin   60           if overMin lt 0               overMin   overMin 60              overHour   overHour-Math floor overMin 60                     newMin   String  overMin lt 10  0      overMin           addHour   addHour overHour       else          newMin   minutes addMin          newMin   String  newMin lt 10  0      newMin               set hour     if   hours addHour gt  13      hours addHour lt  0             overHour    hours addHour  12          ndble   Math floor Math abs  hours addHour  12            if overHour lt  0               newHour   overHour 12              if overHour    0                   ndble                           else              if overHour   0                    newHour   12                  ndble                 else                  ndble                    newHour   overHour                                  newHour    newHour lt 10  0      String newHour           AM     ndble 1  2   0  AM  AM       else          AM    hours addHour  12  AM AM           newHour   String  Number hours  addHour lt 10  0       hours addHour              var am    AM   AM   PM       return new Array newHour  newMin  am        This can be used without parameters to get the current time  getTime      or with parameters to get the time with the added minutes hours  getTime 1 30      adds 1 5 hours to current time getTime 2         adds 2 hours to current time getTime 0 120      same as above   even negative time works  getTime -1  -30      subtracts 1 5 hours from current time   this function returns an array of   array  Hour    Minute    Meridian

[javascript] Adding hours to JavaScript Date object?

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