feat: add warning in dev mode when method is not function (#…

src/core/instance/state.js

@@ -269,6 +269,11 @@ function initMethods (vm: Component, methods: Object) {
           `Did you reference the function correctly?`,
           vm
         )
+      } else if (typeof methods[key] !== 'function') {
+        warn(
+          `Method "${key}" should be a function.`
+        )
+        methods[key] = null
       }
       if (props && hasOwn(props, key)) {
         warn(

test/unit/features/options/methods.spec.js

@@ -37,7 +37,7 @@ describe('Options methods', () => {
         foo () {}
       }
     })
-    expect(`Method "foo" has already been defined as a data property`).toHaveBeenWarned()
+    expect('Method "foo" has already been defined as a data property').toHaveBeenWarned()
   })
 
   it('should warn methods conflicting with internal methods', () => {
@@ -46,6 +46,15 @@ describe('Options methods', () => {
         _update () {}
       }
     })
-    expect(`Method "_update" conflicts with an existing Vue instance method`).toHaveBeenWarned()
+    expect('Method "_update" conflicts with an existing Vue instance method').toHaveBeenWarned()
+  })
+
+  it('should warn if method is not a function', () => {
+    new Vue({
+      methods: {
+        notAFunction: {}
+      }
+    })
+    expect('Method "notAFunction" should be a function').toHaveBeenWarned()
   })
 })