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学习要点:
1.watch
本节课我们来要了解一下 Vue3.x 中的侦听 watch 的用法;
一.watch
1. 在 watch 和在传统的 options 选项对象配置是一样的,具体如下:
(1) . 侦听特定的数据源(watchEffect 是收集依赖式);
(2) . 副作用在第二参数回调执行,并且是懒执行(数据源发生变更);
(3) . 可以访问当前更变的值和上一次变更前的值;
// 这里的 count.vaue 表示要监听的数据源
watch(() => count.value, (count, prevCount) => {
// 在这里执行副作用,参数 1,2 为新旧值
console.log('count:', count, 'prevCount:', prevCount)
})
PS:参数 1,也可以使用 return 返回的方式;
watch(() => {
return count.value
},... 2. 如果想要使用 watch 侦听多个数据源,具体格式如下:
watch([count, name], ([count, prevCount], [name, prevName]) => {...
PS:在侦听的第一个参数,如果没有使用箭头函数,会自动展开.value;