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[Vue.js 3.0] Guide – Components In-Depth – Non-Prop Attributes

# Non-Prop Attributes

This page assumes you’ve already read the Components Basics. Read that first if you are new to components.

A component non-prop attribute is an attribute or event listener that is passed to a component, but does not have a corresponding property defined in props or emits. Common examples of this include class, style, and id attributes. You can access those attributes via $attrs property.

# Attribute Inheritance

When a component returns a single root node, non-prop attributes will automatically be added to the root node’s attributes. For example, in the instance of a date-picker component:

app.component('date-picker', {
template: `
<div class="date-picker">
<input type="datetime" />
</div>
`
})

In the event we need to define the status of the date-picker component via a data-status property, it will be applied to the root node (i.e., div.date-picker).

<!-- Date-picker component with a non-prop attribute -->
<date-picker data-status="activated"></date-picker>
<!-- Rendered date-picker component -->
<div class="date-picker" data-status="activated">
<input type="datetime" />
</div>

Same rule applies to the event listeners:

<date-picker @change="submitChange"></date-picker>
app.component('date-picker', {
created() {
console.log(this.$attrs) // { onChange: () => {}  }
}
})

This might be helpful when we have an HTML element with change event as a root element of date-picker.

app.component('date-picker', {
template: `
<select>
<option value="1">Yesterday</option>
<option value="2">Today</option>
<option value="3">Tomorrow</option>
</select>
`
})

In this case, change event listener is passed from the parent component to the child and it will be triggered on native <select> change event. We won’t need to emit an event from the date-picker explicitly:

<div id="date-picker" class="demo">
<date-picker @change="showChange"></date-picker>
</div>
const app = Vue.createApp({
methods: {
showChange(event) {
console.log(event.target.value) // will log a value of the selected option
}
}
})

# Disabling Attribute Inheritance

If you do not want a component to automatically inherit attributes, you can set inheritAttrs: false in the component’s options.

The common scenario for disabling an attribute inheritance is when attributes need to be applied to other elements besides the root node.

By setting the inheritAttrs option to false, you can control to apply to other elements attributes to use the component’s $attrs property, which includes all attributes not included to component props and emits properties (e.g., class, style, v-on listeners, etc.).

Using our date-picker component example from the previous section, in the event we need to apply all non-prop attributes to the input element rather than the root div element, this can be accomplished by using the v-bind shortcut.

 
app.component('date-picker', {
inheritAttrs: false,
template: `
<div class="date-picker">
<input type="datetime" v-bind="$attrs" />
</div>
`
})

With this new configuration, our data-status attribute will be applied to our input element!

<!-- Date-picker component with a non-prop attribute -->
<date-picker data-status="activated"></date-picker>
<!-- Rendered date-picker component -->
<div class="date-picker">
<input type="datetime" data-status="activated" />
</div>

# Attribute Inheritance on Multiple Root Nodes

Unlike single root node components, components with multiple root nodes do not have an automatic attribute fallthrough behavior. If $attrs are not bound explicitly, a runtime warning will be issued.

<custom-layout id="custom-layout" @click="changeValue"></custom-layout>
// This will raise a warning
app.component('custom-layout', {
template: `
<header>...</header>
<main>...</main>
<footer>...</footer>
`
})
// No warnings, $attrs are passed to <main> element
app.component('custom-layout', {
template: `
<header>...</header>
<main v-bind="$attrs">...</main>
<footer>...</footer>
`
})

炫意HTML5 » [Vue.js 3.0] Guide – Components In-Depth – Non-Prop Attributes

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