// 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 })