# Watch on Arrays
breaking
# Overview
- BREAKING: When watching an array, the callback will only trigger when the array is replaced. If you need to trigger on mutation, the
deep
option must be specified.
# 3.x Syntax
When using the watch
option to watch an array, the callback will only trigger when the array is replaced. In other words, the watch callback will no longer be triggered on array mutation. To trigger on mutation, the deep
option must be specified.
watch: {
bookList: {
handler(val, oldVal) {
console.log('book list changed')
},
deep: true
},
}
1
2
3
4
5
6
7
8
2
3
4
5
6
7
8
# Migration Strategy
If you rely on watching array mutations, add the deep
option to ensure that your callback is triggered correctly.