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Weekly Vue News #108

Manually Stop Watcher

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Vue Tip: Manually Stop Watcher

Vue automatically stops watchers (watch and watchEffect) when the component is unmounted if they are created synchronously in <script setup> or setup().

The following watcher will automatically be stopped if Component.vue is unmounted:

Component.vue


          1 <script setup>

          2 import { watchEffect } from 'vue'

          3 

          4 watchEffect(() => {})

          5 </script>

However, if you create a watcher asynchronously, it will not be stopped automatically:

Component.vue


          1 <script setup>

          2 import { watchEffect, ref } from 'vue'

          3 

          4 const user = ref(null)

          5 

          6 fetchUser().then((userResponse) => {

          7   user.value = userResponse

          8 

          9   // ⚠️ watchEffect is created asynchronously

          10   watchEffect(() => {

          11     if (user.value) {

          12       // do something with the user

          13     }

          14   })

          15 })

          16 </script>

In this case, you can manually stop the watcher by calling the stop function that is returned by watchEffect:

Component.vue


          1 <script setup>

          2 import { watchEffect, ref } from 'vue'

          3 

          4 const user = ref(null)

          5 let unwatch = null

          6 

          7 fetchUser().then((userResponse) => {

          8   user.value = userResponse

          9   unwatch = watchEffect(() => {

          10     if (user.value) {

          11       // do something with the user

          12     }

          13   })

          14 })

          15 

          16 const stopWatcher = () => {

          17   unwatch()

          18 }

          19 </script>

You should prefer creating watchers synchronously and only in rare cases create them asynchronously.

Unstopped watchers can lead to memory leaks and unexpected behavior.

In our example, we could create the watcher synchronously and watch the user ref instead:

Component.vue


          1 <script setup>

          2 import { watchEffect, ref } from 'vue'

          3 

          4 const user = ref(null)

          5 

          6 fetchUser().then((userResponse) => {

          7   user.value = userResponse

          8 })

          9 

          10 watchEffect(() => {

          11   if (user.value) {

          12     // do something with the user

          13   }

          14 })

          15 </script>

This way, the watcher is automatically stopped and you don't need to worry about stopping the watcher yourself.

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📕 JavaScript waitFor Polling

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📕 Just normal web things

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🛠️ screenlog.js

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👉🏻 It can be handy if you have ever struggled to fit your website and browser developer console in the same window.

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🛠️ Knip

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🛠️ continue

👉🏻 Continue is an open-source VS Code extension that brings the power of ChatGPT to your IDE

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🛠️ little-rat

👉🏻 Small chrome extension to monitor other extensions' network calls

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Comments? Join the discussion about this issue here.

Until next week,

Michael Hoffmann (Curator)

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