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A non-prop attribute is an attribute that is passed to a component, but does not have a corresponding prop defined. While explicitly defined props are preferred for passing information to a child component, authors of component libraries can’t always foresee the contexts in which their components might be used. I am trying to create a component that accepts an object as prop and can modify different properties of that object and return the value to the parent, using either sync or emit events. Slots are a powerful tool for creating reusable components in Vue.js, though they aren’t the simplest feature to understand. Let’s take a look at how to use slots and some examples of how they can be used in your Vue applications.

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

Slot Content

Vue implements a content distribution API that’s modeled after the current Web Components spec draft, using the <slot> element to serve as distribution outlets for content.

This allows you to compose components like this:

Then in the template for <navigation-link>, you might have:

When the component renders, the <slot> element will be replaced by “Your Profile”. Slots can contain any template code, including HTML:

Or even other components:

If <navigation-link> did not contain a <slot> element, any content passed to it would simply be discarded.

Named Slots

There are times when it’s useful to have multiple slots. For example, in a hypothetical base-layout component with the following template:

For these cases, the <slot> element has a special attribute, name, which can be used to define additional slots:

To provide content to named slots, we can use the slot attribute on a <template> element in the parent:

Or, the slot attribute can also be used directly on a normal element:

There can still be one unnamed slot, which is the default slot that serves as a catch-all outlet for any unmatched content. In both examples above, the rendered HTML would be:

Default Slot Content

There are cases when it’s useful to provide a slot with default content. For example, a <submit-button> component might want the content of the button to be “Submit” by default, but also allow users to override with “Save”, “Upload”, or anything else.

To achieve this, specify the default content in between the <slot> tags.

If the slot is provided content by the parent, it will replace the default content.

Compilation Scope

When you want to use data inside a slot, such as in:

That slot has access to the same instance properties (i.e. the same “scope”) as the rest of the template. The slot does not have access to <navigation-link>‘s scope. For example, trying to access url would not work. As a rule, remember that:

Everything in the parent template is compiled in parent scope; everything in the child template is compiled in the child scope.

Scoped Slots

New in 2.1.0+

Sometimes you’ll want to provide a component with a reusable slot that can access data from the child component. For example, a simple <todo-list> component may contain the following in its template:

But in some parts of our app, we want the individual todo items to render something different than just the todo.text. This is where scoped slots come in.

To make the feature possible, all we have to do is wrap the todo item content in a <slot> element, then pass the slot any data relevant to its context: in this case, the todo object:

Now when we use the <todo-list> component, we can optionally define an alternative <template> for todo items, but with access to data from the child via the slot-scope attribute:

In 2.5.0+, slot-scope is no longer limited to the <template> element, but can instead be used on any element or component in the slot.

Destructuring slot-scope

The value of slot-scope can actually accept any valid JavaScript expression that can appear in the argument position of a function definition. This means in supported environments (single-file components or modern browsers) you can also use ES2015 destructuring in the expression, like so:

This is a great way to make scoped slots a little cleaner.

You’re browsing the documentation for v2.x and earlier. For v3.x, click here.

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

Prop Casing (camelCase vs kebab-case)

HTML attribute names are case-insensitive, so browsers will interpret any uppercase characters as lowercase. That means when you’re using in-DOM templates, camelCased prop names need to use their kebab-cased (hyphen-delimited) equivalents:

Again, if you’re using string templates, this limitation does not apply.

Prop Types

So far, we’ve only seen props listed as an array of strings:

Usually though, you’ll want every prop to be a specific type of value. In these cases, you can list props as an object, where the properties’ names and values contain the prop names and types, respectively:

This not only documents your component, but will also warn users in the browser’s JavaScript console if they pass the wrong type. You’ll learn much more about type checks and other prop validations further down this page.

Passing Static or Dynamic Props

So far, you’ve seen props passed a static value, like in:

You’ve also seen props assigned dynamically with v-bind, such as in:

In the two examples above, we happen to pass string values, but any type of value can actually be passed to a prop.

Passing a Number

Passing a Boolean

Passing an Array

Passing an Object

Passing the Properties of an Object

If you want to pass all the properties of an object as props, you can use v-bind without an argument (v-bind instead of v-bind:prop-name). For example, given a post object:

The following template:

Will be equivalent to:

One-Way Data Flow

All props form a one-way-down binding between the child property and the parent one: when the parent property updates, it will flow down to the child, but not the other way around. This prevents child components from accidentally mutating the parent’s state, which can make your app’s data flow harder to understand.

In addition, every time the parent component is updated, all props in the child component will be refreshed with the latest value. This means you should not attempt to mutate a prop inside a child component. If you do, Vue will warn you in the console.

There are usually two cases where it’s tempting to mutate a prop:

1. The prop is used to pass in an initial value; the child component wants to use it as a local data property afterwards. In this case, it’s best to define a local data property that uses the prop as its initial value:

2. The prop is passed in as a raw value that needs to be transformed. In this case, it’s best to define a computed property using the prop’s value:

Note that objects and arrays in JavaScript are passed by reference, so if the prop is an array or object, mutating the object or array itself inside the child component will affect parent state.

Prop Validation

Components can specify requirements for their props, such as the types you’ve already seen. If a requirement isn’t met, Vue will warn you in the browser’s JavaScript console. This is especially useful when developing a component that’s intended to be used by others.

To specify prop validations, you can provide an object with validation requirements to the value of props, instead of an array of strings. For example:

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When prop validation fails, Vue will produce a console warning (if using the development build).

Note that props are validated before a component instance is created, so instance properties (e.g. data, computed, etc) will not be available inside default or validator functions.

Type Checks

The type can be one of the following native constructors:

• String
• Number
• Boolean
• Array
• Object
• Date
• Function
• Symbol

In addition, type can also be a custom constructor function and the assertion will be made with an instanceof check. For example, given the following constructor function exists:

You could use:

to validate that the value of the author prop was created with new Person.

Non-Prop Attributes

A non-prop attribute is an attribute that is passed to a component, but does not have a corresponding prop defined.

While explicitly defined props are preferred for passing information to a child component, authors of component libraries can’t always foresee the contexts in which their components might be used. That’s why components can accept arbitrary attributes, which are added to the component’s root element.

For example, imagine we’re using a 3rd-party bootstrap-date-input component with a Bootstrap plugin that requires a data-date-picker attribute on the input. We can add this attribute to our component instance:

And the data-date-picker='activated' attribute will automatically be added to the root element of bootstrap-date-input.

Replacing/Merging with Existing Attributes

Imagine this is the template for bootstrap-date-input:

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To specify a theme for our date picker plugin, we might need to add a specific class, like this:

In this case, two different values for class are defined:

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• form-control, which is set by the component in its template
• date-picker-theme-dark, which is passed to the component by its parent

For most attributes, the value provided to the component will replace the value set by the component. So for example, passing type='text' will replace type='date' and probably break it! Fortunately, the class and style attributes are a little smarter, so both values are merged, making the final value: form-control date-picker-theme-dark.

Disabling Attribute Inheritance

If you do not want the root element of a component to inherit attributes, you can set inheritAttrs: false in the component’s options. For example:

This can be especially useful in combination with the $attrs instance property, which contains the attribute names and values passed to a component, such as:

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With inheritAttrs: false and $attrs, you can manually decide which element you want to forward attributes to, which is often desirable for base components:

Note that inheritAttrs: false option does not affect style and class bindings.

This pattern allows you to use base components more like raw HTML elements, without having to care about which element is actually at its root: