Fix negative event.timeStamp values on iOS 11.3

[lasselaakkonen]

#549

[lwenke]

The comment said "iOS 11.3 returns negative values for event.timeStamp after pausing/resuming a Cordova application". If that is true, what about this fix?
touchStartTime = (event.timeStamp < 0) ? (new Date()).getTime() : event.timeStamp;

[lasselaakkonen]

That would also work, it would have the benefit of not having to detect platforms and hope for the best.

There is an unlikely edge case where it will fail, when event.timeStamp changes from negative to positive, but even that could be worked around by doing touchEndTime = (event.timeStamp < 0 || event.timeStamp < this.trackingClickStart ? (new Date()).getTime() : event.timeStamp) or by saving the source of the touch start timestamp (event vs Date) in onTouchStart and using the same source in onTouchEnd. Does that edge case matter for FastClick?

Normally the timestamps would increment like 3,4,5,6,7,.. but then at some point for some reason iOS starts returning them like this -4,-3,-2,-1,0,1,2,3,4,.. so the timestamps will at some point jump from negative to positive and then with (event.timeStamp < 0) ? (new Date()).getTime() : event.timeStamp FastClick will end up comparing a very large number ((new Date()).getTime()) and a lot smaller number (event.timeStamp, which on iOS seems to be some kind of "milliseconds since this session started" counter).

Should I change it like this?

    if (event.timeStamp < 0) {
      touchStartTime = (new Date()).getTime();
    } else {
      touchStartTime = event.timeStamp;
    }
    ...
    this.trackingClickStart = touchStartTime;

    if (event.timeStamp < 0 || event.timeStamp < this.trackingClickStart) {
      touchEndTime = (new Date()).getTime();
    } else {
      touchEndTime = event.timeStamp;
    }

Or simply check for event.timeStamp < 0?

[lwenke]

Sorry I don't really understand what is going on in the code but it would be really good if you could update it soon so that it works for iOS 11.4+ as well (if the problem is still there) so that if people download the fixed version of the app it would also work if they updated it to iOS 11.4.

I guess it would be good to take into account that edge case too.

[lasselaakkonen]

Sorry, the consecutive integers were a bit confusing, it was just to illustrate that the numbers are integers and increment from 0 -> +INT or -INT -> +INT.

On iOS event.timeStamp values are milliseconds since something.

[lwenke]

Thanks for your code above - I edited the code using it.

[gwynjudd]

Is it possible for event.timeStamp to be positive for the touchstart event but negative for the touchend event? In which case, it would be better to only use (new Date()).getTime() instead of the event.timeStamp.

Otherwise, the comparisons below would cause the touchend to exit early:

 		// Prevent phantom clicks on fast double-tap (issue #36)
 		if ((touchEndTime - this.lastClickTime) < this.tapDelay) {

[mantovanig]

Please Merge!! 🙏 @JakeChampion

[danicholls]

This is one of the few areas where this library is really needed. Would be great to get this fix merged in!

[caoweiju]

look at this: Events can have a negative timestamp which causes app breakage -- webkit's bug