fix: use single object prop on

feat: provide hasMetaInfo export for other libraries to check if metaInfo has been defined

chore: deprecate _hasMetaInfo

test/plugin-server.test.js

@@ -1,4 +1,4 @@
-import { mount, defaultOptions, VueMetaServerPlugin, loadVueMetaPlugin } from './utils'
+import { mount, defaultOptions, hasMetaInfo, VueMetaServerPlugin, loadVueMetaPlugin } from './utils'
 
 jest.mock('../package.json', () => ({
   version: 'test-version'
@@ -7,6 +7,7 @@ jest.mock('../package.json', () => ({
 describe('plugin', () => {
   let Vue
 
+  beforeEach(() => jest.clearAllMocks())
   beforeAll(() => (Vue = loadVueMetaPlugin()))
 
   test('is loaded', () => {
@@ -29,4 +30,43 @@ describe('plugin', () => {
   test('plugin sets package version', () => {
     expect(VueMetaServerPlugin.version).toBe('test-version')
   })
+
+  test('prints deprecation warning once when using _hasMetaInfo', () => {
+    const warn = jest.spyOn(console, 'warn').mockImplementation(() => {})
+
+    const Component = Vue.component('test-component', {
+      template: '<div>Test</div>',
+      [defaultOptions.keyName]: {
+        title: 'Hello World'
+      }
+    })
+
+    Vue.config.devtools = true
+    const { vm } = mount(Component, { localVue: Vue })
+
+    expect(vm._hasMetaInfo).toBe(true)
+    expect(warn).toHaveBeenCalledTimes(1)
+
+    expect(vm._hasMetaInfo).toBe(true)
+    expect(warn).toHaveBeenCalledTimes(1)
+    warn.mockRestore()
+  })
+
+  test('can use hasMetaInfo export', () => {
+    const warn = jest.spyOn(console, 'warn').mockImplementation(() => {})
+
+    const Component = Vue.component('test-component', {
+      template: '<div>Test</div>',
+      [defaultOptions.keyName]: {
+        title: 'Hello World'
+      }
+    })
+
+    const { vm } = mount(Component, { localVue: Vue })
+
+    expect(hasMetaInfo(vm)).toBe(true)
+    expect(warn).not.toHaveBeenCalled()
+
+    warn.mockRestore()
+  })
 })