Generalize suppression of undesired default behaviors when dragging.

[mbostock]

Fixes #1321.

[tpreusse]

this change broke common, documented usage of force.drag

node
    .on('click', function(d) {
        // do something
    })
    .call(force.drag);

now needs to be:

node
    .on('touchstart', function(d) {
        d3.event.preventDefault(); // no scrolling
    })
    .on('click', function(d) {
        if(!d3.event.defaultPrevented) {
            // do something
        }
    })
    .call(force.drag);

However I do like the change. Not sure about the right approach to patching this: patch layout/force.js (at least touchstart would seem reasonable) and or create some awareness for the breaking change - update docu, examples etc.

[mbostock]

I don’t think you need the d3.event.defaultPrevented check; it’s still the case that the drag behavior will suppress clicks when the node is dragged.

But you are correct that we no longer preventDefault on touchstart… We decided we didn’t want to disable the browser behaviors by default, since it’s impossible to undo the effect of preventing the default behavior, but it’s always possible to prevent it in your own code. On the other hand, we do prevent selectstart and dragstart events, so I do wonder whether there’s a way to disable scrolling here.

Ugh, browser events.

[tpreusse]

!d3.event.defaultPrevented is needed because default gets prevented but propagation still happens - my click listener gets called with a default prevented event.

[mbostock]

Ah, you’re right. We just preventDefault on that click, not stopPropagation.

[tpreusse]

yeah it's quite tricky but checking for d3.event.defaultPrevented is not a major hassle and gives you full control - just needs to be documented (if desired). Btw.: I upgraded specifically to get the touchend with force.drag for a tooltip - which is nice and was really hard before.