那么Vue中data数据改变后会触发几次render呢

// 实例化一个Watcher对象，收集data和computedData相关的所有数据依赖
// 一旦有变动，则触发调用vm.render
vm.renderWatcher = new Watcher(
vm,
(() => {
    // 简单粗暴但是有问题
    // 比如data变动触发diff重绘和computedData的重新计算
    // computedData可能还有变动，然后又一次触发diff重绘
    walk(data); // 递归遍历data的所有属性
    walk(computedData);
}),
vm.render,
);

} else {
  updateComponent = () => {
    vm._update(vm._render(), hydrating)
  }
}

// we set this to vm._watcher inside the watcher's constructor
// since the watcher's initial patch may call $forceUpdate (e.g. inside child
// component's mounted hook), which relies on vm._watcher being already defined
new Watcher(vm, updateComponent, noop, {
  before () {
    if (vm._isMounted && !vm._isDestroyed) {
      callHook(vm, 'beforeUpdate')
    }
  }
}, true /* isRenderWatcher */)

// 重绘触发
vm.renderWatcher = new Watcher(vm, vm.render, () => 1);

// ...
export default {
  data(){
    return {
      btnClickCount: 0,
      otherData: '',
    }
  },
  methods:{
    onBtnClick(){
      this.btnClickCount = this.btnClickCount + 1;
      this.otherData = this.otherData + 'jkhas';
    },
  }
};

/**
  * Subscriber interface.
  * Will be called when a dependency changes.
  */
update () {
  /* istanbul ignore else */
  if (this.lazy) {
    this.dirty = true
  } else if (this.sync) {
    this.run()
  } else {
    queueWatcher(this)
  }
}

/**
 * Push a watcher into the watcher queue.
 * Jobs with duplicate IDs will be skipped unless it's
 * pushed when the queue is being flushed.
 */
export function queueWatcher (watcher: Watcher) {
  const id = watcher.id
  if (has[id] == null) {
    has[id] = true
    if (!flushing) {
      queue.push(watcher)
    } else {
      // if already flushing, splice the watcher based on its id
      // if already past its id, it will be run next immediately.
      let i = queue.length - 1
      while (i > index && queue[i].id > watcher.id) {
        i--
      }
      queue.splice(i + 1, 0, watcher)
    }
    // queue the flush
    if (!waiting) {
      waiting = true

      if (process.env.NODE_ENV !== 'production' && !config.async) {
        flushSchedulerQueue()
        return
      }
      nextTick(flushSchedulerQueue)
    }
  }
}