How to run a Javascript alert every Friday at 16:00

Question

Is this possible using setInterval()?

In the below example, the alert is every 5 seconds...

<script type="text/javascript">
  setInterval(function() {
    // alert("Message to alert every 5 seconds");
}, 5000);
</script>

I'm trying to run safari push notification inside the interval function, maybe it isn't the best practice, but it's a workaround for now

function Notifier() {}

    // Returns "true" if this browser supports notifications.
    Notifier.prototype.HasSupport = function() {
      if (window.webkitNotifications) {
        return true;
      } else {
        return false;
      }
    }

    // Request permission for this page to send notifications. If allowed,
    // calls function "cb" with true.
    Notifier.prototype.RequestPermission = function(cb) {
      window.webkitNotifications.requestPermission(function() {
        if (cb) { cb(window.webkitNotifications.checkPermission() == 0); }
      });
    }

    // Popup a notification with icon, title, and body. Returns false if
    // permission was not granted.
    Notifier.prototype.Notify = function(icon, title, body) {
      if (window.webkitNotifications.checkPermission() == 0) {
        var popup = window.webkitNotifications.createNotification(
        icon, title, body);
        popup.show();

        return true;
      }

      return false;
    }

    $(function() {
      var notifier = new Notifier();
      if (!notifier.HasSupport()) {
        $("#error").show();
        return;
      }

      $("#request-permission").click(function() {
        $("#error").hide();
        notifier.RequestPermission();
      });

      $(function() {
        if (!notifier.Notify("#", "MESSAGE")) {
          $("#error").text('Permission denied. Click "Request Permission" to give this domain access to send notifications to your desktop.');
          $("#error").show();
        } else {
          $("#error").hide();
        }
      });
    });

It's more like a math problem here :)) how many milliseconds between each Fridays 16:00 — NinjaShawarma, Jan 07 '17 at 16:33
@j08691 I need this alert to run every Friday at 16:00 does it make sense at your end? — NinjaShawarma, Jan 07 '17 at 16:35
This would only make sense if the website is open for a looooooooooong time. — simbabque, Jan 07 '17 at 16:37
You need Date calculations, setInterval() will not help here... — sinisake, Jan 07 '17 at 16:37
@simbabque fair enough, the website is open everyday. And to be exact I'm not running an alert. I'm running a Safari push notification. — NinjaShawarma, Jan 07 '17 at 16:38
I have edited the question to make it clear enough @sinisake — NinjaShawarma, Jan 07 '17 at 16:41
I have edited the question to make it clear enough @simbabque — NinjaShawarma, Jan 07 '17 at 16:42
This cannot work unless the website stays open forever. If that is the case (which I highly doubt), then there are so many ways of doing it. — Neville, Jan 07 '17 at 17:03

MarioZ · Accepted Answer · 2017-01-07T16:52:19.087

2

You can use something like:

<script type="text/javascript">
    var date = new Date();
    console.log(date.getDay());
    console.log(date.getHours());
    if(date.getDay() === 6 && date.getHours() === 17) {
        console.log("HELLO WORLD!");
    }
</script>

getDay() returns the day of the week from 1 to 7 (friday would be a 5) and getHours() returns the hour from 1 to 24. You can continue from here :)

Update: this checks the date every 5 seconds with setInterval() if that's what you need:

<script type="text/javascript">

function checkDate() {
    var date = new Date();
    console.log(date.getDay());
    console.log(date.getHours());
    if(date.getDay() === 6 && date.getHours() === 17) {
        console.log("HELLO WORLD!");
    }
}

var dateLoop = setInterval(function() {
    checkDate();
},5000);
</script>

edited Jan 07 '17 at 16:52

answered Jan 07 '17 at 16:45

MarioZ

981
7
16

And then run it in a loop? – simbabque Jan 07 '17 at 16:45
Yes, whatever you need to do you can put this inside a function that runs in an interval loop, or with other event that works. – MarioZ Jan 07 '17 at 16:48
Running it all the time sounds very expensive. Well, maybe when you run it once a minute it would be ok. It certainly is more of the brute force approach compared to actually calculating next Friday. – simbabque Jan 07 '17 at 16:49

score 0 · Answer 2 · edited May 23 '17 at 12:33

Disclaimer: this answer only describes the needed algorithm.

First, you need to assume the browser window with the website stays open until Friday. If not, this is useless and you probably don't want to do this on a website.

If you still want to go ahead, you need to create a new Date object where you find the next Friday at 4pm. You would have to take into account the timezone. Do you want GMT, or the server's timezone, or a fixed one, or the user's timezone (and do you even know that?) Then you have to calculate the difference between that timestamp and now. Convert that to milliseconds and set your interval.

There are several good answers on how to obtain a future date with a certain weekday in Get date of specific day of the week in JavaScript. From there, you only need to do some basic calculations.

The approach I described here does not change with your clarifications @NinjaShawarma. — simbabque, Jan 07 '17 at 16:45

myfunkyside · Answer 3 · 2017-01-07T17:09:27.590

0

You could just check every second if the day, hours, minutes and seconds match Friday 16:00:00

window.onload = function() {
  setInterval(function() {
    var date = new Date();
    if (date.getDay()==5 && date.getHours()==16 && date.getMinutes()==0 && date.getSeconds()==0) {
      alert("4 O'CLOCK!");
    }
  },1000);
};

jsfiddle: https://jsfiddle.net/dwdek28r/1/

Not sure if it's recommendable though..

edited Jan 07 '17 at 17:09

answered Jan 07 '17 at 16:50

myfunkyside

3,890
1
17
32

score 0 · Answer 4 · answered Jan 07 '17 at 16:50

0

Hope it helps.

 var dayOfWeek = 5; // friday
 var date = new Date();
 date.setDate(date.getDate() + (dayOfWeek + 7 - date.getDay()) % 7);
 date.setHours(16,0,0,0)

 var dif = date.getTime() - new Date().getTime();
 console.log(dif);

 setTimeout(function () {
    // send alert or push notification

 }, dif);

answered Jan 07 '17 at 16:50

Engin

755
7
20

This keeps sending the Timeout function no matter what the setHours() is. Just for the sake of trying the function, I changed the dayOfWeek to 6 which is Sat. See https://jsfiddle.net/15p21uxv/ Let me know what you think. Thanks! – NinjaShawarma Jan 07 '17 at 18:48

How to run a Javascript alert every Friday at 16:00

4 Answers4