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Vue Answers

How directly change state with Vue Vuex?

To directly change state with Vue and Vuex, we should use mutations. Mutations are synchronous functions responsible for modifying the state in a Vuex store.

To directly change state using mutations, we:

  1. Define a mutation in our Vuex store.
  2. Commit the mutation from our Vue components.

For example, we write

// store.js
import Vue from 'vue';
import Vuex from 'vuex';

Vue.use(Vuex);

const store = new Vuex.Store({
  state: {
    counter: 0
  },
  mutations: {
    increment(state) {
      state.counter++;
    },
    decrement(state) {
      state.counter--;
    },
    setCounter(state, value) {
      state.counter = value;
    }
  }
});

export default store;

In our Vue component:

<template>
  <div>
    <p>Counter: {{ counter }}</p>
    <button @click="increment">Increment</button>
    <button @click="decrement">Decrement</button>
    <button @click="setCounter(0)">Reset</button>
  </div>
</template>

<script>
import { mapState, mapMutations } from 'vuex';

export default {
  computed: {
    ...mapState(['counter'])
  },
  methods: {
    ...mapMutations(['increment', 'decrement', 'setCounter'])
  }
};
</script>

In this example we have a Vuex store with a counter state and mutations to increment, decrement, and set the counter.

In the Vue component, we use mapState to map the counter state from the Vuex store to a computed property.

We use mapMutations to map the mutations from the Vuex store to methods in the component.

We can then call these methods directly from the component to modify the state in the Vuex store.

By using mutations, we ensure that state changes are tracked, debuggable, and predictable.

Vuex enforces the principle of a single state tree and mutations being the only way to change the state, which helps manage state changes in a large application.

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Vue Answers

How to watch height of an element in Vue.js?

To watch the height of an element in Vue.js, we can use a combination of a ref and a watcher.

For instance we write:

<template>
  <div ref="elementToWatch" style="border: 1px solid black; overflow: hidden;">
    <!-- Content that may affect the height of the element -->
  </div>
</template>

<script>
export default {
  mounted() {
    this.$nextTick(() => {
      // Watch the height of the element
      this.watchElementHeight();
    });
  },
  methods: {
    watchElementHeight() {
      const element = this.$refs.elementToWatch;
      
      // Create a new MutationObserver to watch for changes in the height of the element
      const observer = new MutationObserver(mutations => {
        mutations.forEach(mutation => {
          // Trigger some action when the height of the element changes
          console.log('Element height changed:', element.clientHeight);
        });
      });
      
      // Configure the MutationObserver to observe changes in the attributes and childList of the target node
      const config = { attributes: true, childList: true, subtree: true };
      
      // Start observing the target node for configured mutations
      observer.observe(element, config);
    }
  }
};
</script>

In this example we use a ref (elementToWatch) to access the element whose height we want to watch.

  • We use mounted lifecycle hook to ensure that the element is available in the DOM before we attempt to watch its height.

Inside the watchElementHeight method, we create a new MutationObserver to observe mutations on the target element.

We configure the MutationObserver to observe changes in attributes, child nodes, and subtree of the target node.

We define a callback function that will be executed whenever a mutation is observed. In this callback, we can perform actions based on changes in the height of the element.

Finally, we call observe on the MutationObserver instance to start observing the target node for mutations.

This setup allows we to watch for changes in the height of the target element and trigger actions accordingly.

Adjust the actions inside the MutationObserver callback as needed based on our specific requirements.

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Vue Answers

How to show state with arrow with Bootstrap-vue Collapse?

To show the state (open or closed) of a Bootstrap-vue Collapse component with an arrow indicating whether it’s expanded or collapsed, we can use some CSS and Vue.js to dynamically apply classes to the arrow element based on the collapse state.

For instance we write:

<template>
  <div>
    <b-button v-b-toggle.collapse1 variant="primary">Toggle Collapse</b-button>
    <b-collapse id="collapse1" v-model="isOpen">
      <div class="collapse-content">
        <!-- Our content here -->
      </div>
    </b-collapse>
  </div>
</template>

<script>
export default {
  data() {
    return {
      isOpen: false
    };
  }
};
</script>

<style>
.collapse-arrow {
  transition: transform 0.3s ease;
}
.collapse-arrow.collapsed {
  transform: rotate(-90deg);
}
</style>

In this example we’re using Bootstrap-vue’s Collapse component to toggle the visibility of content.

The collapse arrow is implemented using CSS and Vue.js to apply a rotation when the collapse is open or closed.

The v-b-toggle directive on the button toggles the visibility of the collapse.

The v-model directive on the collapse binds its visibility state to the isOpen data property.

We can customize the arrow styling and animation according to our design preferences. Adjust the classes and styles as needed to match our application’s design.

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Vue Answers

How to fix “The specified key does not exist” error for Vue.js app deployed on deployed on S3 with CloudFront?

If you’re encountering “The specified key does not exist” error for a Vue.js app deployed on S3 with CloudFront, it’s likely due to CloudFront caching or misconfiguration. Here are some steps to troubleshoot and fix the issue:

1. Check S3 Bucket Configuration

Ensure that your S3 bucket is configured correctly to serve your Vue.js files. Make sure the files are uploaded to the correct path in the bucket and have the correct permissions.

2. Invalidate CloudFront Cache

If you’ve recently updated your Vue.js files, CloudFront might be serving stale content from its cache.

Try invalidating the CloudFront cache to force it to fetch fresh content from your S3 bucket.

To do this:

  • Go to the CloudFront console.
  • Select your distribution.
  • In the “Invalidations” tab, create a new invalidation for the path of your Vue.js files (e.g., /index.html or /*).
  • Confirm the invalidation.

3. Check CloudFront Origin Settings

Ensure that the CloudFront distribution is configured to use the correct origin (your S3 bucket) and that the origin settings are configured correctly.

To do this:

  • Go to the CloudFront console.
  • Select your distribution.
  • Check the “Origins and Origin Groups” tab to ensure that the origin points to the correct S3 bucket and the correct path.
  • Verify the origin settings, such as origin protocol policy, origin access identity, etc.

4. Check CloudFront Behavior Settings

Verify the behavior settings in your CloudFront distribution to ensure they are configured correctly for your Vue.js application.

To do this

  • Go to the CloudFront console.
  • Select your distribution.
  • Check the “Behaviors” tab.
  • Ensure that the caching behavior is configured appropriately (e.g., caching behavior for static assets, TTL settings).
  • Verify that the “Default Root Object” is set to index.html or your desired entry point.

5. Verify DNS Configuration:

Ensure that your DNS settings are correctly configured to point to your CloudFront distribution. If you’re using a custom domain, verify that the DNS records are correctly set up to resolve to the CloudFront distribution.

6. Check Vue Router Configuration:

If you’re using Vue Router and encountering this issue when navigating to specific routes, ensure that your Vue Router configuration is correct. Make sure that the routes defined in Vue Router match the paths served by your S3 bucket and CloudFront distribution.

By following these steps, you should be able to troubleshoot and fix the “The specified key does not exist” error for your Vue.js app deployed on S3 with CloudFront.

Categories
Vue Answers

How to dynamically change a CSS class after a scroll position with Vue.js?

We can dynamically change a CSS class based on the scroll position using Vue.js by utilizing a combination of data properties, computed properties, and event listeners.

Below is a basic example of how to achieve this:

<template>
  <div :class="{ 'scrolled': isScrolled }">
    <!-- Our content here -->
  </div>
</template>

<script>
export default {
  data() {
    return {
      isScrolled: false
    };
  },
  mounted() {
    window.addEventListener('scroll', this.handleScroll);
  },
  beforeDestroy() {
    window.removeEventListener('scroll', this.handleScroll);
  },
  methods: {
    handleScroll() {
      // Calculate scroll position
      const scrollPosition = window.scrollY || window.pageYOffset;
      
      // Update isScrolled based on scroll position
      this.isScrolled = scrollPosition > 0;
    }
  }
};
</script>

<style>
/* Define our CSS classes */
.scrolled {
  /* Our styles for scrolled state */
}
</style>

In this example we have a div element whose class is bound dynamically using the :class directive.

The class scrolled will be applied when the isScrolled property is true.

We listen for the scroll event on the window object and call the handleScroll method.

Inside the handleScroll method, we calculate the scroll position using window.scrollY or window.pageYOffset.

Based on the scroll position, we update the isScrolled property, which in turn updates the CSS class dynamically.

Adjust the scroll position threshold or add additional logic in the handleScroll method as needed to fit our specific requirements.