make vm.$watch api consistent with watch option (vuejs#5645)

src/core/instance/state.js

@@ -247,16 +247,20 @@ function initWatch (vm: Component, watch: Object) {
  }
 }
 
-function createWatcher (vm: Component, key: string, handler: any) {
- let options
+function createWatcher (
+ vm: Component,
+ keyOrFn: string | Function,
+ handler: any,
+ options?: Object
+) {
  if (isPlainObject(handler)) {
  options = handler
  handler = handler.handler
  }
  if (typeof handler === 'string') {
  handler = vm[handler]
  }
- vm.$watch(key, handler, options)
+ return vm.$watch(keyOrFn, handler, options)
 }
 
 export function stateMixin (Vue: Class<Component>) {
@@ -287,10 +291,13 @@ export function stateMixin (Vue: Class<Component>) {
 
  Vue.prototype.$watch = function (
  expOrFn: string | Function,
- cb: Function,
+ cb: any,
  options?: Object
  ): Function {
  const vm: Component = this
+ if (isPlainObject(cb)) {
+ return createWatcher(vm, expOrFn, cb, options)
+ }
  options = options || {}
  options.user = true
  const watcher = new Watcher(vm, expOrFn, cb, options)

test/unit/features/instance/methods-data.spec.js

@@ -21,14 +21,17 @@ describe('Instance methods data', () => {
  describe('$watch', () => {
  let vm, spy
  beforeEach(() => {
+ spy = jasmine.createSpy('watch')
  vm = new Vue({
  data: {
  a: {
  b: 1
  }
+ },
+ methods: {
+ foo: spy
  }
  })
- spy = jasmine.createSpy('watch')
  })
 
  it('basic usage', done => {
@@ -81,6 +84,30 @@ describe('Instance methods data', () => {
  }).then(done)
  })
 
+ it('handler option', done => {
+ var oldA = vm.a
+ vm.$watch('a', {
+ handler: spy,
+ deep: true
+ })
+ vm.a.b = 2
+ waitForUpdate(() => {
+ expect(spy).toHaveBeenCalledWith(oldA, oldA)
+ vm.a = { b: 3 }
+ }).then(() => {
+ expect(spy).toHaveBeenCalledWith(vm.a, oldA)
+ }).then(done)
+ })
+
+ it('handler option in string', () => {
+ vm.$watch('a.b', {
+ handler: 'foo',
+ immediate: true
+ })
+ expect(spy.calls.count()).toBe(1)
+ expect(spy).toHaveBeenCalledWith(1)
+ })
+
  it('warn expresssion', () => {
  vm.$watch('a + b', spy)
  expect('Watcher only accepts simple dot-delimited paths').toHaveBeenWarned()