Bug while calling e.preventDefault

[slorber]

I have this: <Tappable onTap={this.onTap}>{element}</Tappable>;

When my listener is:

    onTap: function(e) {
        console.error("tap!",e);
        e.preventDefault();
        this.props.onTap(e);
    },

I get an error:

tap! SyntheticTouchEvent {dispatchConfig: null, dispatchMarker: null, nativeEvent: null, type: null, target: null…} touchable.jsx:22
Uncaught TypeError: Cannot read property 'preventDefault' of null 

It is not the e that is null, but calling e.preventDefault(); calls this internal SyntheticTouchEvent function:

  preventDefault: function() {
    this.defaultPrevented = true;
    var event = this.nativeEvent;
    if (event.preventDefault) {
      event.preventDefault();
    } else {
      event.returnValue = false;
    }
    this.isDefaultPrevented = emptyFunction.thatReturnsTrue;
  },

This is related to how React use pooling on Synthetic events and because onTap is called asynchronously un the setState callback

[slorber]

The React Synthetic events loose their native events while handled in async callbacks because I think they are resetted and put in the pool.

    endTouch: function endTouch(event, callback) {
        this.cancelPressDetection();
        this.clearActiveTimeout();
        if (event && this.props.onTouchEnd) {
            this.props.onTouchEnd(event);
        }
        this._initialTouch = null;
        this._lastTouch = null;
        if (this.state.isActive) {
            this.setState({
                isActive: false
            }, callback);
        } else if (callback) {
            callback();
        }
    },

The problem is because the callback of setState() is called asynchronously.

This works fine for me:

    endTouch: function endTouch(event, callback) {
        this.cancelPressDetection();
        this.clearActiveTimeout();
        if (event && this.props.onTouchEnd) {
            this.props.onTouchEnd(event);
        }
        this._initialTouch = null;
        this._lastTouch = null;
        if (this.state.isActive) {
            callback();
            this.setState({
                isActive: false
            });
        } else if (callback) {
            callback();
        }
    },

[slorber]

See PR #47

[slorber]

Also I think it should be documented that preventDefault is already called on the event before the onTap is called so it means I don't need to call it myself

[slorber]

A temporary workaround is to access the nativeEvent through the "onTouchEnd" callback which is called synchronously

So if you want to stop propagation of the touchend event in onTap (preventDefault is done, but not stopPropagation), instead you can do:

<Tappable onTap={this.props.onTap} onTouchEnd={function(e) { e.stopPropagation() }}>{element}</Tappable>;

I think this should be possible to handle directly in onTap(e) and this is what my PR solves

[slorber]

@JedWatson notice that when using React.Perf I'm also having an error in Perf code that only appears when using onTap of tappable (see facebook/react#3389 (comment))

Surprisingly, my PR also solves this problem (but I absolutly don't know why)

[slorber]

@JedWatson btw another possible fix if you still want to use the setState callback (not sure it's a good idea however) you can use event.persist()

[JedWatson]

@slorber this should be resolved now that your PR has been merged, let me know if you can still reproduce any issues relating to it.