Remove listener for window events when unbinding Vue directive lifecycle

Question

Remove listener for window events when unbinding Vue directive lifecycle

I recently encountered a problem concerning event listening in Vue directives. Within my component, I have the following code:

function setHeaderWrapperHeight() { ... }
function scrollEventHandler() { ... }

export default {
  ...
  directives: {
    fox: {
      inserted(el, binding, vnode) {
        setHeaderWrapperHeight(el);
        el.classList.add('header__unfixed');
        window.addEventListener(
          'scroll',
          scrollEventListener.bind(null, el, binding.arg)
        );
        window.addEventListener(
          'resize',
          setHeaderWrapperHeight.bind(null, el)
        );
      },
      unbind(el, binding) {
        console.log('Unbound');
        window.removeEventListener('scroll', scrollEventListener);
        window.removeEventListener('resize', setHeaderWrapperHeight);
      }
    }
  }
  ...
}

Every time I change the router path, this component is re-rendered by assigning the current route path to the :key prop. However, the issue lies in the fact that the event listeners are not being removed or destroyed, causing significant performance problems. How can I properly remove these event listeners?

javascript vue.js vue-directives

Answer 1

Answer №1

element, it is explained that calling the bind function on a function generates a new function, which leads to listeners not being removed due to passing a different function to removeEventListener than what was initially passed to addEventListener. While communicating between hooks in directives may pose some challenges, the official suggestion is to utilize the element's dataset, although this may appear clumsy in certain scenarios. Instead, storing listeners directly as properties on the element can make them accessible in the unbind hook. An alternative approach presented involves using an array to keep track of all elements currently bound to the directive. By registering the listener on window once, even if the directive is used multiple times, and removing the listener when the directive is not in use. It is also mentioned that using a directive may not always be necessary and handling things at the component level could simplify matters since the component instance can store information. It is crucial to remember that creating a new function upon calling bind necessitates saving a reference to that function for later removal with removeEventListener.

Answer 2

element, it is explained that calling the bind function on a function generates a new function, which leads to listeners not being removed due to passing a different function to removeEventListener than what was initially passed to addEventListener. While communicating between hooks in directives may pose some challenges, the official suggestion is to utilize the element's dataset, although this may appear clumsy in certain scenarios. Instead, storing listeners directly as properties on the element can make them accessible in the unbind hook. An alternative approach presented involves using an array to keep track of all elements currently bound to the directive. By registering the listener on window once, even if the directive is used multiple times, and removing the listener when the directive is not in use. It is also mentioned that using a directive may not always be necessary and handling things at the component level could simplify matters since the component instance can store information. It is crucial to remember that creating a new function upon calling bind necessitates saving a reference to that function for later removal with removeEventListener.

Answer 3

Answer №2

Just wanted to share some insights for those who may stumble upon this post in the future, even though there is already an answer provided. In the context of Vue 3 (not tested on Vue 2), one approach worth considering is utilizing binding.dir as a reference to the directive's object. This allows you to store and retrieve event listener functions associated with the directive.

As a simple illustration (unrelated to the original topic) of binding a focus event:

export default {
  ...
  directives: {
    fox: {
      handleFocus: () => { /* placeholder code */ },
      mounted(el, binding) {
        binding.dir.handleFocus = () => { /* actual action */ }
        el.addEventListener('focus', binding.dir.handleFocus);
      },
      beforeUnmount(el, binding) {
        el.removeEventListener('focus', binding.dir.handleFocus);
      }
    }
  }
  ...
}

An application example of this concept in use would be creating a focus/blur notifier for input or textarea elements. I have shared a Gist here showcasing how I implemented it in a Vue 3 project using TypeScript.

Answer 4

Just wanted to share some insights for those who may stumble upon this post in the future, even though there is already an answer provided. In the context of Vue 3 (not tested on Vue 2), one approach worth considering is utilizing binding.dir as a reference to the directive's object. This allows you to store and retrieve event listener functions associated with the directive.

As a simple illustration (unrelated to the original topic) of binding a focus event:

export default {
  ...
  directives: {
    fox: {
      handleFocus: () => { /* placeholder code */ },
      mounted(el, binding) {
        binding.dir.handleFocus = () => { /* actual action */ }
        el.addEventListener('focus', binding.dir.handleFocus);
      },
      beforeUnmount(el, binding) {
        el.removeEventListener('focus', binding.dir.handleFocus);
      }
    }
  }
  ...
}

An application example of this concept in use would be creating a focus/blur notifier for input or textarea elements. I have shared a Gist here showcasing how I implemented it in a Vue 3 project using TypeScript.

Answer 5

Answer №3

In this code snippet, I have implemented a solution for adding and removing an event listener on the window to handle resizing events. ChatGPT provided some assistance in optimizing the functionality:

  .component('resizeHandler', {
    beforeMount(el, binding, vnode) {
      const resizeCallback = binding.value;
      window.addEventListener('resize', () => {
        const width = document.documentElement.clientWidth;
        const height = document.documentElement.clientHeight;
        resizeCallback({ width, height });
      }, { passive: true });
      // eslint-disable-next-line no-underscore-dangle, no-param-reassign
      el._resizeListener = binding.value;
    },
    unmounted(el) {
      // eslint-disable-next-line no-underscore-dangle
      window.removeEventListener('resize', el._resizeListener);
    },
  })

Answer 6

In this code snippet, I have implemented a solution for adding and removing an event listener on the window to handle resizing events. ChatGPT provided some assistance in optimizing the functionality:

  .component('resizeHandler', {
    beforeMount(el, binding, vnode) {
      const resizeCallback = binding.value;
      window.addEventListener('resize', () => {
        const width = document.documentElement.clientWidth;
        const height = document.documentElement.clientHeight;
        resizeCallback({ width, height });
      }, { passive: true });
      // eslint-disable-next-line no-underscore-dangle, no-param-reassign
      el._resizeListener = binding.value;
    },
    unmounted(el) {
      // eslint-disable-next-line no-underscore-dangle
      window.removeEventListener('resize', el._resizeListener);
    },
  })

Remove listener for window events when unbinding Vue directive lifecycle

Answer №1

Answer №2

Answer №3

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