How to use the new v-slot directive in Vue.js

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Last week the version 2.6.0-beta.3 of Vue.js was released, enabling a new feature to simplify scoped slots even more.

It introduces the new v-slot directive and its shorthand, as described in the RFC-0001 and RFC-0002.

In order to understand how it does simplify the syntax, let's see how's it in current scoped slots. Imagine you have a List the component that exposes a filtered list as its scope.

The way you'd use that List scoped slot would be similar to:

<template>
  <List :items="items">
    <template slot-scope="{ filteredItems }">
      <p v-for="item in filteredItems" :key="item">{{ item }}</p>
    </template>
  </List>
</template>

The implementation of the List component is not too relevant, but in this Codesandbox you can check an example of it.

With v-slot, you can write the scope of that slot directly on the component tag, avoiding an extra layer:

<template>
  <List v-slot="{ filteredItems }" :items="items">
    <p v-for="item in filteredItems" :key="item">{{ item }}</p>
  </List>
</template>

Keep in mind v-slot can only be used on components and template tags, but not in plain HTML tags

This makes the code more readable specially when you have nested scoped slots, which can be difficult to reason where a scope comes from.

The v-slot directive also introduces a way to combine the slot and the scoped-slots directive, but by separating them with a colon :.

For example, this example taken from vue-promised:

<template>
  <Promised :promise="usersPromise">
    <p slot="pending">Loading...</p>

    <ul slot-scope="users">
      <li v-for="user in users">{{ user.name }}</li>
    </ul>

    <p slot="rejected" slot-scope="error">Error: {{ error.message }}</p>
  </Promised>
</template>

Could be written with v-slot as follows:

<template>
  <Promised :promise="usersPromise">
    <template v-slot:pending>
      <p>Loading...</p>
    </template>

    <template v-slot="users">
      <ul>
        <li v-for="user in users">{{ user.name }}</li>
      </ul>
    </template>

    <template v-slot:rejected="error">
      <p>Error: {{ error.message }}</p>
    </template>
  </Promised>
</template>

And to end up, v-slot has the symbol # as a shorthand, so the example before could be written as:

<template>
  <Promised :promise="usersPromise">
    <template #pending>
      <p>Loading...</p>
    </template>

    <template #default="users">
      <ul>
        <li v-for="user in users">{{ user.name }}</li>
      </ul>
    </template>

    <template #rejected="error">
      <p>Error: {{ error.message }}</p>
    </template>
  </Promised>
</template>

Just keep in mind that the shorthand for the default v-slot is #default.

Are you excited about this new slot syntax?

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