Adding support for zIndex

Author: mzabriskie

lib/draggable.js

@@ -103,6 +103,25 @@ module.exports = React.createClass({
 		 */
 		cancel: React.PropTypes.string,
 
+		/**
+		 * `zIndex` to use while dragging.
+		 *
+		 * Example:
+		 *
+		 * ```jsx
+		 * 	var App = React.createClass({
+		 * 	    render: function () {
+		 * 	        return (
+		 * 	            <Draggable zIndex={100}>
+		 * 	                <div>I have a zIndex</div>
+		 * 	            </Draggable>
+		 * 	        );
+		 * 	    }
+		 * 	});
+		 * ```
+		 */
+		zIndex: React.PropTypes.number,
+
 		/**
 		 * Called when dragging starts.
 		 *
@@ -169,6 +188,7 @@ module.exports = React.createClass({
 			axis: 'both',
 			handle: null,
 			cancel: null,
+			zIndex: NaN,
 			onStart: emptyFunction,
 			onDrag: emptyFunction,
 			onStop: emptyFunction
@@ -241,6 +261,10 @@ module.exports = React.createClass({
 			left: canDragX(this) ? this.state.clientX : this.state.startX
 		};
 
+		if (this.state.dragging && !isNaN(this.props.zIndex)) {
+			style.zIndex = this.props.zIndex;
+		}
+
 		// Reuse the child provided
 		// This makes it flexible to use whatever element is wanted (div, ul, etc)
 		var child = null;