RE: [JSMentors] Image polling through Javascript

[Joel Dart]

You also probably have a helper method in your base library, for example in 
jQuery, jQuery.now() wraps (new Date()).getTime()

-----Original Message-----
From: jsmentors@googlegroups.com [mailto:jsment...@googlegroups.com] On Behalf 
Of Ben Barber
Sent: Monday, December 20, 2010 12:23 PM
To: jsmentors@googlegroups.com
Subject: Re: [JSMentors] Image polling through Javascript

I'm a fan of using implicit number conversion on Dates using the unary '+'  
operator (http://xkr.us/articles/javascript/unary-add/).

    "http://....gif?"; + ( +new Date() );


Ben Barber


On Mon, 20 Dec 2010 04:44:44 -0600, Amit Agarwal <lifea...@gmail.com>
wrote:

> yeah, I liked the timestamp concept.
>
> Modified my code and worked perfectly :)
>
> Thanks!
>
> -Regards
> *Amit Agarwal <http:///www.amitagrwal.com>*
> +91-779-822-8765
>
>
>
> On Mon, Dec 20, 2010 at 3:35 PM, Shane Tomlinson <set...@gmail.com>
> wrote:
>
>> I personally like to use timestamps over ints or rand, a timestamp is 
>> ensured to be unique.  If you use an int and in this session you had 
>> "http://.....gif?1";, the next time the user goes into the app, they 
>> re-use the integer 1, using the cache.  And Math.random isn't as 
>> random as you want it to be:
>> http://stackoverflow.com/questions/1062902/how-random-is-javascripts-math-random.
>>  But a timestamp, that is going to be unique unless you reset your 
>> system's clock.
>>
>> And performance wise, trying to optimize this is a 
>> premature-optimization.
>>  Unless your request is called many many thousands of times a second, 
>> the performance overhead of using a timestamp will be effectively 0.
>>
>> Check out:
>> https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/
>> Date/getTime, this returns the number of milliseconds since Jan 1, 
>> 1970, again, unless the user resets their system clock, it is 
>> guaranteed to be unique.
>>
>> try requesting: "http://....gif?"; + ( new Date() ).getTime();
>>
>>
>> On Mon, Dec 20, 2010 at 9:45 AM, Loic Giraudel
>> <l.girau...@gmail.com>wrote:
>>
>>> Or for better performance a simple incremented int variable.
>>>
>>>
>>> On Mon, Dec 20, 2010 at 10:43, fernando trasvina
>>> <trasv...@gmail.com>wrote:
>>>
>>>> use ?Math.random() on ur uri
>>>> or timestamp + Math.random()
>>>>
>>>> On Dec 20, 2010, at 3:35 AM, Amit Agarwal wrote:
>>>>
>>>> Hi every one,
>>>>
>>>> I need to poll an image using javascript and need to perform an 
>>>> action once the image is found at its position. This is the code I 
>>>> have written for this task.
>>>>
>>>> /*----Image handling script starts here----*/ var beacon = new 
>>>> Image();
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> beacon.onload = function() {
>>>>
>>>>
>>>>     console.log('Image found');
>>>>     console.log(this.width,this.height);
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>     window.clearInterval(timer);
>>>> };
>>>>
>>>>
>>>> beacon.onerror = function(){
>>>>    console.log('Image not found');
>>>>
>>>>
>>>>
>>>>
>>>> }
>>>> var timer = window.setInterval(function(){
>>>>
>>>>
>>>>     console.log('sending the request again');
>>>>     beacon.src = 
>>>> "http://www.google.co.in/logos/2010/lennon10-hp.gif";;
>>>>
>>>>
>>>>
>>>>
>>>> },2000);
>>>> /*----Image handling script ends here----*/
>>>>
>>>> Problem is that, after one GET request, the response gets cached 
>>>> and requests don't get sent everytime I set src. If you examine NET 
>>>> tab, it sends request only on first src set and caches the 
>>>> response.
>>>>
>>>> I need to send a fresh request for image every time my code sets 
>>>> the src.
>>>> Any workarounds?
>>>>
>>>> -Regards
>>>> *Amit Agarwal <http:/www.amitagrwal.com>*
>>>> +91-779-822-8765
>>>>
>>>>
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