In iOS Safari, the first click event may not work when a DOM change occurs

[shinsenter]

Issue

Issue #121:
In iOS Safari, the first click event may not work when using Defer.all() with the waitForUserAction argument set to true and one of deferred scripts make any DOM change.

Bug Detail

When a waitForUserAction or the Defer.lazy option is set to true, Defer.js attaches a touchstart event on the window element to track user interaction and execute lazied script tags.

Let's suppose the user touches a link in mobile browser. Because the user has the ability to double tap to zoom or scroll, whenever the user touches the screen, the browser does not instantaneously know whether the user meant to click the link, or is double tapping. Therefore every mobile browser adds a 300ms delay onto tap interactions to see if the user taps again.

Touch gestures handled by Safari on iOS emulate mouse events. When you touch an iPhone’s screen, in principle Safari responds by firing an entire event cascade:

1. touchstart
2. touchend
3. mouseover
4. mousemove
5. mousedown
6. mouseup
7. click

But during the touch event cascade, Safari iOS stops firing click events when a DOM change takes place.

Apple's Figure 6-4: One-finger gesture emulating a mouse

Source: Safari Web Content Guide

Temporary solutions

Add a pause at least 300ms to the Defer.all(). For example: Defer.all('script[type="your-type"]', 500, true);.