fix: setState callback should emit in willMount

see detail in the test case

Author: yuche

packages/nerv/__tests__/lifecycle.spec.js

@@ -238,6 +238,36 @@ describe('Lifecycle methods', () => {
       expect(spy.calledOnce).toBe(true)
     })
 
+    it('setState in setState callback should work in componentWillMount', () => {
+      const spy = sinon.spy()
+      class App extends Component {
+        constructor (props) {
+          super(props)
+          this.state = {
+            msg: ''
+          }
+        }
+
+        componentWillMount () {
+          this.setState({
+            msg: 'test'
+          }, () => {
+            this.setState({
+              msg: 'test2'
+            }, () => {
+              spy()
+            })
+          })
+        }
+        render () {
+          return <div>{this.state.msg}</div>
+        }
+      }
+
+      render(<App />, scratch)
+      expect(spy.calledOnce).toBe(true)
+    })
+
     it('get latest state', () => {
       class App extends Component {
         constructor (props) {

packages/nerv/src/component.ts

@@ -86,10 +86,11 @@ class Component<P, S> implements ComponentInst<P, S> {
 
   clearCallBacks () {
     // cached the length of callbacks, or callbacks may increase by calling them in the same loop
-    const len = this._pendingCallbacks.length
-    for (let i = 0; i < len; i++) {
+    let len = this._pendingCallbacks.length
+    while (this._dirty ? this._pendingCallbacks.length : len) {
       const cb = this._pendingCallbacks.shift()!
       cb.call(this)
+      len--
     }
   }