Dragging

D3 has two built in function for behaviours:

• Drag — tracks mouse or multitouch movement(s) relative to an origin
• Zoom — emits zoom and pan events in response to common input idioms

Drag Events

When a drag event listener is invoked, it receives the current drag event as its first argument. The event object exposes several fields:

• target - the associated drag behavior.
• type - the string "start", "drag" or "end"; see drag.on.
• subject - the drag subject, defined by drag.subject.
• x - the new x-coordinate of the subject; see drag.container.
• y - the new y-coordinate of the subject; see drag.container.
• dx - the change in x-coordinate since the previous drag event.
• dy - the change in y-coordinate since the previous drag event.
• identifier - the string "mouse", or a numeric touch identifier.
• active - the number of currently active drag gestures (on start and end, not including this one).
• sourceEvent - the underlying input event, such as mousemove or touchmove.