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Update WATCH_ARRAY recommendations to use deep: 1 #70

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Update WATCH_ARRAY recommendations to use deep: 1 #70

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11 changes: 10 additions & 1 deletion src/breaking-changes/watch.md
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,8 @@ badges:
## 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.
- In Vue 3.5+, `deep: 1` should be used, which will trigger on array replacement and array mutation.
- Prior to Vue 3.5, `deep: true` can be used, but it will also trigger on deep changes in array elements.

## 3.x Syntax

Expand All @@ -20,11 +22,18 @@ watch: {
handler(val, oldVal) {
console.log('book list changed')
},
deep: true
deep: 1 // Vue 3.5+
deep: true // Vue 3.0 - 3.4
},
}
```

:::warning

In versions prior to Vue 3.5, watches don't allow setting the [max traversal depth](https://vuejs.org/guide/essentials/watchers.html#deep-watchers), so you're stuck with `deep: true`, which will also trigger the callback on deep modification of array elements.

:::

## Migration Strategy

If you rely on watching array mutations, add the `deep` option to ensure that your callback is triggered correctly.
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