Add $.fn.preempt, which runs the given event handler before any others.

spec/stdlib/jquery-extensions-spec.coffee

@@ -0,0 +1,25 @@
+$ = require 'jquery'
+
+describe 'jQuery extensions', ->
+  describe '$.fn.preempt(eventName, handler)', ->
+    [returnValue, element, events] = []
+
+    beforeEach ->
+      element = $("<div>")
+      events = []
+
+      element.on 'foo', -> events.push(1)
+      element.preempt 'foo', ->
+        events.push(2)
+        returnValue
+      element.on 'foo', -> events.push(3)
+
+    it 'calls the preempting handler before all others', ->
+      element.trigger 'foo'
+      expect(events).toEqual [2,1,3]
+
+    describe 'when handler returns false', ->
+      it 'does not call subsequent handlers', ->
+        returnValue = false
+        element.trigger 'foo'
+        expect(events).toEqual [2]

src/stdlib/jquery-extensions.coffee

@@ -14,3 +14,10 @@ $.fn.scrollRight = (newValue) ->
 
 $.fn.containsElement = (element) ->
   (element[0].compareDocumentPosition(this[0]) & 8) == 8
+
+$.fn.preempt = (eventName, handler) ->
+  @on eventName, (e) ->
+    if handler() == false then e.stopImmediatePropagation()
+
+  handlers = @data('events')[eventName]
+  handlers.unshift(handlers.pop())