侦测变化 - watch

Watch 文档地址

// watch 简单应用
watch(data, () => {
  document.title = 'updated ' + data.count
})
// watch 的两个参数，代表新的值和旧的值
watch(refData.count, (newValue, oldValue) => {
  console.log('old', oldValue)
  console.log('new', newValue)
  document.title = 'updated ' + data.count
})

// watch 多个值，返回的也是多个值的数组
watch([greetings, data], (newValue, oldValue) => {
  console.log('old', oldValue)
  console.log('new', newValue)
  document.title = 'updated' + greetings.value + data.count
})

// 使用 getter 的写法 watch reactive 对象中的一项
watch([greetings, () => data.count], (newValue, oldValue) => {
  console.log('old', oldValue)
  console.log('new', newValue)
  document.title = 'updated' + greetings.value + data.count
})