Merge pull request #7360 from atom/iz-blow-up-on-undefined-command-callback

Throw error for commands registered with non-function callbacks

spec/command-registry-spec.coffee

@@ -158,6 +158,26 @@ describe "CommandRegistry", ->
         addError = error
       expect(addError.message).toContain(badSelector)
 
+    it "throws an error when called with a non-function callback and selector target", ->
+      badCallback = null
+      addError = null
+
+      try
+        registry.add '.selector', 'foo:bar', badCallback
+      catch error
+        addError = error
+      expect(addError.message).toContain("Can't register a command with non-function callback.")
+
+    it "throws an error when called with an non-function callback and object target", ->
+      badCallback = null
+      addError = null
+
+      try
+        registry.add document.body, 'foo:bar', badCallback
+      catch error
+        addError = error
+      expect(addError.message).toContain("Can't register a command with non-function callback.")
+
   describe "::findCommands({target})", ->
     it "returns commands that can be invoked on the target or its ancestors", ->
       registry.add '.parent', 'namespace:command-1', ->

src/command-registry.coffee

@@ -92,6 +92,9 @@ class CommandRegistry
         disposable.add @add(target, commandName, callback)
       return disposable
 
+    if typeof callback isnt 'function'
+      throw new Error("Can't register a command with non-function callback.")
+
     if typeof target is 'string'
       validateSelector(target)
       @addSelectorBasedListener(target, commandName, callback)