fix #4872, use context agnostic Function constructor check

src/core/util/props.js

@@ -70,7 +70,8 @@ function getPropDefaultValue (vm: ?Component, prop: PropOptions, key: string): a
     return vm[key]
   }
   // call factory function for non-Function types
-  return typeof def === 'function' && prop.type !== Function
+  // a value is Function if its prototype is function even across different execution context
+  return typeof def === 'function' && getType(prop.type) !== 'Function'
     ? def.call(vm)
     : def
 }

test/ssr/ssr-string.spec.js

@@ -1,4 +1,5 @@
 import Vue from '../../dist/vue.runtime.common.js'
+import VM from 'vm'
 import { createRenderer } from '../../packages/vue-server-renderer'
 const { renderToString } = createRenderer()
 
@@ -699,6 +700,23 @@ describe('SSR: renderToString', () => {
       done()
     }, context)
   })
+
+  it('default value Foreign Function', () => {
+    const FunctionConstructor = VM.runInNewContext('Function')
+    const func = () => 123
+    const vm = new Vue({
+      props: {
+        a: {
+          type: FunctionConstructor,
+          default: func
+        }
+      },
+      propsData: {
+        a: undefined
+      }
+    })
+    expect(vm.a).toBe(func)
+  })
 })
 
 function renderVmWithOptions (options, cb) {

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

@@ -98,6 +98,22 @@ describe('Options props', () => {
     }).then(done)
   })
 
+  it('default value Function', () => {
+    const func = () => 132
+    const vm = new Vue({
+      props: {
+        a: {
+          type: Function,
+          default: func
+        }
+      },
+      propsData: {
+        a: undefined
+      }
+    })
+    expect(vm.a).toBe(func)
+  })
+
   it('warn object/array default values', () => {
     new Vue({
       props: {