If you are building a webapp which is dependent on time (for example, a bidding or betting application) then you must have seen the requirement to show time on the webapp depending on the timezone of the logged in user. The other day i was going through various blogs and i saw a couple of posts by different blogs covering this approach and i was amazed to see that how complex route they took. So, i thought to write a post describing some really easy steps to achieve this.
There are multiple decisions/questions that you have to answer in order to achieve this goal.
1. In what timezone will you save the time in your db?
2. How would you get user's timezone?
3. When do you want to change the timezone according to user's timezone?
In this post i'll go through each of the above questions one by one.
In order to answer the first question, the best option is to go for GMT/UTC timezone. The reason is that it's extremely easy to convert time from GMT to GMT+8 or GMT0-5 etc. You can simply add/subtract the difference from the timestamp. But, you have to consider another thing here, if you are hosting your webapp on a shared server, then you need to consider the timestamp your shared hosting server is using. Because for any time critical webapp, you'll be frequently getting the current time and the server will be returning you the timestamp depending on the timezone it has set. Most of the shared hosting servers don't allow you to change the timezone. Now, you can also keep GMT/UTC timezone as the default timezone and you can change the timezone of the current time as well. Both are valid ways, so it's up to you what to go for. Now, whenever user enters some datetime, you convert the datetime entered into the default timezone and save it in your db.
Now, the second question, i.e. how would you get user's timezone. Now there are a couple of ways to achieve this.
1. Ask the user for his timezone upon registration and use that
This is a fairly popular and accurate method of getting user's timestamp. The only problem in this approach is that it's not dynamic, i.e. if the user moves to a different timezone, he'll have to manually change his timezone on your webapp. If you don't mind putting your users through this step, then this method is recommended.
2. Get the timezone from the ip of the user
This is another method of getting the timezone of the logged in user. You can use ip of the user to track his geolocation and from that you can determine his timezone. Though, personally i don't think this is a good approach to go for. In my personal opinion it looks like an over kill unless you are already tracking and showing data on the basis of user's geolocation.
3. Get the timezone of the user through javascript.
I personally like this method because of its simplicity. You can easily get the timezone of the logged in user through following steps.
session_start();
$_SESSION['userTimeZone'] = $_GET['utz'];
?>
Now, you have user's timezone saved in session. Whenever, you want to display a time, simply convert the stored time into user's timezone. Now, again there are multiple ways to achieve this. One very simple way is to save user's timezone in terms of seconds and simply add/subtract from the stored timestamp (if you used GMT as your default timezone). Or, you can use the following code to achieve this as well. (in order to use the following code you need to save user's timezone in proper format i.e. GMT+2)
And there you go, it's as simple as that.
There are multiple decisions/questions that you have to answer in order to achieve this goal.
1. In what timezone will you save the time in your db?
2. How would you get user's timezone?
3. When do you want to change the timezone according to user's timezone?
In this post i'll go through each of the above questions one by one.
In order to answer the first question, the best option is to go for GMT/UTC timezone. The reason is that it's extremely easy to convert time from GMT to GMT+8 or GMT0-5 etc. You can simply add/subtract the difference from the timestamp. But, you have to consider another thing here, if you are hosting your webapp on a shared server, then you need to consider the timestamp your shared hosting server is using. Because for any time critical webapp, you'll be frequently getting the current time and the server will be returning you the timestamp depending on the timezone it has set. Most of the shared hosting servers don't allow you to change the timezone. Now, you can also keep GMT/UTC timezone as the default timezone and you can change the timezone of the current time as well. Both are valid ways, so it's up to you what to go for. Now, whenever user enters some datetime, you convert the datetime entered into the default timezone and save it in your db.
Now, the second question, i.e. how would you get user's timezone. Now there are a couple of ways to achieve this.
1. Ask the user for his timezone upon registration and use that
This is a fairly popular and accurate method of getting user's timestamp. The only problem in this approach is that it's not dynamic, i.e. if the user moves to a different timezone, he'll have to manually change his timezone on your webapp. If you don't mind putting your users through this step, then this method is recommended.
2. Get the timezone from the ip of the user
This is another method of getting the timezone of the logged in user. You can use ip of the user to track his geolocation and from that you can determine his timezone. Though, personally i don't think this is a good approach to go for. In my personal opinion it looks like an over kill unless you are already tracking and showing data on the basis of user's geolocation.
3. Get the timezone of the user through javascript.
I personally like this method because of its simplicity. You can easily get the timezone of the logged in user through following steps.
- Get the timezone of the logged in user on your main page. For this i saw such complex approaches that i was amazed. Certainly some people love to bring gun to a knife fight :s .You can achieve this through one line of the following code
- - (new Date.getTimezoneOffset()/60)
- This method basically returns the difference between GMT and local time in minutes. So, if you are at GMT+2 then Date.getTimezoneOffset() will return -120 and if you are at GMT-2 then it will return 120. Therefore, simply put a - before it and divide the result by 60 and you'll get the time difference in hours.
- Make an ajax call and send this time difference on some server page and store it in session or cookie. A simple snippet of the code is
session_start();
$_SESSION['userTimeZone'] = $_GET['utz'];
?>
Now, you have user's timezone saved in session. Whenever, you want to display a time, simply convert the stored time into user's timezone. Now, again there are multiple ways to achieve this. One very simple way is to save user's timezone in terms of seconds and simply add/subtract from the stored timestamp (if you used GMT as your default timezone). Or, you can use the following code to achieve this as well. (in order to use the following code you need to save user's timezone in proper format i.e. GMT+2)
public function convertTimeZone($date, $from_tz, $to_tz, $dateFormat) {
$dateObj = new DateTime($date, new DateTimeZone($from_tz));
$dateObj->setTimezone(new DateTimeZone($to_tz));
return $dateObj->format($dateFormat);
$dateObj = new DateTime($date, new DateTimeZone($from_tz));
$dateObj->setTimezone(new DateTimeZone($to_tz));
return $dateObj->format($dateFormat);
}
And there you go, it's as simple as that.
