What is Purpose of Keep Alive Tag in Vue.js

The <keep-alive> tag in Vue.js is a built-in component that is used to cache and preserve the state of components that are dynamic and have stateful or costly mounting and unmounting operations. It ensures that components are kept alive and not destroyed when they are toggled using v-if or when they are navigated away from and then back to.

Purpose of <keep-alive>

1. Preserve Component State: When a component is wrapped inside <keep-alive>, its state (such as data, computed properties, and the state of child components) is preserved even when the component is toggled on and off the DOM.
2. Optimize Performance: Components inside <keep-alive> are cached instead of being destroyed and recreated every time they are toggled. This can improve performance, especially for components with expensive initialization or rendering logic.
3. Maintain Component Lifecycle: Components inside <keep-alive> will go through their lifecycle hooks like created, mounted, activated, deactivated, and destroyed as they are toggled in and out of the DOM. This allows you to maintain the integrity of component lifecycle methods.

Example

Here's an example of how you can use <keep-alive> in a Vue.js application.

<template>
  <div>
    <button @click="toggleComponent">Toggle Component</button>
    <keep-alive>
      <component v-if="isActive" :is="currentComponent"></component>
    </keep-alive>
  </div>
</template>

<script>
import ComponentA from './ComponentA.vue';
import ComponentB from './ComponentB.vue';

export default {
  data() {
    return {
      isActive: true,
      currentComponent: 'ComponentA'
    };
  },
  methods: {
    toggleComponent() {
      this.isActive = !this.isActive;
      this.currentComponent = this.isActive ? 'ComponentA' : 'ComponentB';
    }
  },
  components: {
    ComponentA,
    ComponentB
  }
}
</script>

In this example

• We have a parent component that toggles between two child components (ComponentA and ComponentB) using a button.
• The child components are wrapped inside <keep-alive> to preserve their state.
• When toggling, the <component> element with the is attribute is used to dynamically switch between the two child components based on the isActive data property.

Benefits of <keep-alive>

• Improved Performance: Components inside <keep-alive> are not destroyed and re-created every time they are toggled, leading to better performance, especially for complex components.
• Preserved State: The state of components inside <keep-alive> is preserved, allowing users to navigate back to a component without losing any data or user input.
• Component Reusability: <keep-alive> promotes component reusability by allowing you to cache and reuse components in different parts of your application.

Overall, <keep-alive> is a useful feature in Vue.js for optimizing performance and preserving component state in dynamic applications.