Vue Slots Vs Props

1. Vue Slots Vs Props Play
2. Vue Template Slot
3. Vue Slot Or Prop
4. V Slot Vue

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Props work in a very similar way to this. We pass props to another component, and that component can then use that value. But there are a couple rules you need to know about first. Two main characteristics of Vue props. There are two specific things to keep in mind when dealing with props: Props are passed down the component tree to descendents. Create reusable components by learning about the Scoped Slot and Render Props patterns. Grab our biggest discount of the year at 50% off an annual subscription.

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With the recent release of Vue 2.6, the syntax for using slots has been made more succinct. This change to slots has gotten me re-interested in discovering the potential power of slots to provide reusability, new features, and clearer readability to our Vue-based projects. What are slots truly capable of?

If you’re new to Vue or haven’t seen the changes from version 2.6, read on. Probably the best resource for learning about slots is Vue’s own documentation, but I’ll try to give a rundown here.

What Are Slots?

Slots are a mechanism for Vue components that allows you to compose your components in a way other than the strict parent-child relationship. Slots give you an outlet to place content in new places or make components more generic. The best way to understand them is to see them in action. Let’s start with a simple example:

This component has a wrapper div. Let’s pretend that div is there to create a stylistic frame around its content. This component is able to be used generically to wrap a frame around any content you want. Let’s see what it looks like to use it. The frame component here refers to the component we just made above.

The content that is between the opening and closing frame tags will get inserted into the frame component where the slot is, replacing the slot tags. This is the most basic way of doing it. You can also specify default content to go into a slot simply by filling it in:

So now if we use it like this instead:

The default text of “This is the default content if nothing gets specified to go here” will show up, but if we use it as we did before, the default text will be overridden by the img tag.

Multiple/Named Slots

You can add multiple slots to a component, but if you do, all but one of them is required to have a name. If there is one without a name, it is the default slot. Here’s how you create multiple slots:

We kept the same default slot, but this time we added a slot named header where you can enter a title. You use it like this:

Just like before, if we want to add content to the default slot, just put it directly inside the titled-frame component. To add content to a named slot, though, we needed to wrap the code in a template tag with a v-slot directive. You add a colon (:) after v-slot and then write the name of the slot you want the content to be passed to. Note that v-slot is new to Vue 2.6, so if you’re using an older version, you’ll need to read the docs about the deprecated slot syntax.

Scoped Slots

One more thing you’ll need to know is that slots can pass data/functions down to their children. To demonstrate this, we’ll need a completely different example component with slots, one that’s even more contrived than the previous one: let’s sorta copy the example from the docs by creating a component that supplies the data about the current user to its slots:

This component has a property called user with details about the user. By default, the component shows the user’s last name, but note that it is using v-bind to bind the user data to the slot. With that, we can use this component to provide the user data to its descendant:

To get access to the data passed to the slot, we specify the name of the scope variable with the value of the v-slot directive.

There are a few notes to take here:

• We specified the name of default, though we don’t need to for the default slot. Instead we could just use v-slot='slotProps'.
• You don’t need to use slotProps as the name. You can call it whatever you want.
• If you’re only using a default slot, you can skip that inner template tag and put the v-slot directive directly onto the current-user tag.
• You can use object destructuring to create direct references to the scoped slot data rather than using a single variable name. In other words, you can use v-slot='{user}' instead of v-slot='slotProps' and then you can use user directly instead of slotProps.user.

Taking those notes into account, the above example can be rewritten like this:

A couple more things to keep in mind:

Vue Slots Vs Props Play

• You can bind more than one value with v-bind directives. So in the example, I could have done more than just user.
• You can pass functions to scoped slots too. Many libraries use this to provide reusable functional components as you’ll see later.
• v-slot has an alias of #. So instead of writing v-slot:header='data', you can write #header='data'. You can also just specify #header instead of v-slot:header when you’re not using scoped slots. As for default slots, you’ll need to specify the name of default when you use the alias. In other words, you’ll need to write #default='data' instead of #='data'.

There are a few more minor points you can learn about from the docs, but that should be enough to help you understand what we’re talking about in the rest of this article.

What Can You Do With Slots?

Slots weren’t built for a single purpose, or at least if they were, they’ve evolved way beyond that original intention to be a powerhouse tool for doing many different things.

Reusable Patterns

Components were always designed to be able to be reused, but some patterns aren’t practical to enforce with a single “normal” component because the number of props you’ll need in order to customize it can be excessive or you’d need to pass large sections of content and potentially other components through the props. Slots can be used to encompass the “outside” part of the pattern and allow other HTML and/or components to placed inside of them to customize the “inside” part, allowing the component with slots to define the pattern and the components injected into the slots to be unique.

For our first example, let’s start with something simple: a button. Imagine you and your team are using Bootstrap*. With Bootstrap, your buttons are often strapped with the base `btn` class and a class specifying the color, such as `btn-primary`. You can also add a size class, such as `btn-lg`.

* I neither encourage nor discourage you from doing this, I just needed something for my example and it’s pretty well known.

Let’s now assume, for simplicity’s sake that your app/site always uses btn-primary and btn-lg. You don’t want to always have to write all three classes on your buttons, or maybe you don’t trust a rookie to remember to do all three. In that case, you can create a component that automatically has all three of those classes, but how do you allow customization of the content? A prop isn’t practical because a button tag is allowed to have all kinds of HTML in it, so we should use a slot.

Now we can use it everywhere with whatever content you want:

Of course, you can go with something much bigger than a button. Sticking with Bootstrap, let’s look at a modal, or least the HTML part; I won’t be going into functionality… yet.

Now, let’s use this:

The above type of use case for slots is obviously very useful, but it can do even more.

Reusing Functionality

Vue components aren’t all about the HTML and CSS. They’re built with JavaScript, so they’re also about functionality. Slots can be useful for creating functionality once and using it in multiple places. Let’s go back to our modal example and add a function that closes the modal:

Now when you use this component, you can add a button to the footer that can close the modal. Normally, in the case of a Bootstrap modal, you could just add data-dismiss='modal' to a button, but we want to hide Bootstrap specific things away from the components that will be slotting into this modal component. So we pass them a function they can call and they are none the wiser about Bootstrap’s involvement:

Renderless Components

And finally, you can take what you know about using slots to pass around reusable functionality and strip practically all of the HTML and just use the slots. That’s essentially what a renderless component is: a component that provides only functionality without any HTML.

Making components truly renderless can be a little tricky because you’ll need to write render functions rather than using a template in order to remove the need for a root element, but it may not always be necessary. Let’s take a look at a simple example that does let us use a template first, though:

This is an odd example of a renderless component because it doesn’t even have any JavaScript in it. That’s mostly because we’re just creating a pre-configured reusable version of a built-in renderless function: transition.

Yup, Vue has built-in renderless components. This particular example is taken from an article on reusable transitions by Cristi Jora and shows a simple way to create a renderless component that can standardize the transitions used throughout your application. Cristi’s article goes into a lot more depth and shows some more advanced variations of reusable transitions, so I recommend checking it out.

For our other example, we’ll create a component that handles switching what is shown during the different states of a Promise: pending, successfully resolved, and failed. It’s a common pattern and while it doesn’t require a lot of code, it can muddy up a lot of your components if the logic isn’t pulled out for reusability.

So what is going on here? First, note that we are receiving a prop called promise that is a Promise. In the watch section we watch for changes to the promise and when it changes (or immediately on component creation thanks to the immediate property) we clear the state, and call then and catch on the promise, updating the state when it either finishes successfully or fails.

Then, in the template, we show a different slot based on the state. Note that we failed to keep it truly renderless because we needed a root element in order to use a template. We’re passing data and error to the relevant slot scopes as well.

And here’s an example of it being used:

We pass in somePromise to the renderless component. While we’re waiting for it to finish, we’re displaying “Working on it…” thanks to the pending slot. If it succeeds we display “Resolved:” and the resolution value. If it fails we display “Rejected:” and the error that caused the rejection. Now we no longer need to track the state of the promise within this component because that part is pulled out into its own reusable component.

So, what can we do about that span wrapping around the slots in promised.vue? To remove it, we’ll need to remove the template portion and add a render function to our component:

There isn’t anything too tricky going on here. We’re just using some if blocks to find the state and then returning the correct scoped slot (via this.$scopedSlots['SLOTNAME'](...)) and passing the relevant data to the slot scope. When you’re not using a template, you can skip using the .vue file extension by pulling the JavaScript out of the script tag and just plunking it into a .js file. This should give you a very slight performance bump when compiling those Vue files.

This example is a stripped-down and slightly tweaked version of vue-promised, which I would recommend over using the above example because they cover over some potential pitfalls. There are plenty of other great examples of renderless components out there too. Baleada is an entire library full of renderless components that provide useful functionality like this. There’s also vue-virtual-scroller for controlling the rendering of list item based on what is visible on the screen or PortalVue for “teleporting” content to completely different parts of the DOM.

I’m Out

Vue’s slots take component-based development to a whole new level, and while I’ve demonstrated a lot of great ways slots can be used, there are countless more out there. What great idea can you think of? What ways do you think slots could get an upgrade? If you have any, make sure to bring your ideas to the Vue team. God bless and happy coding.

In this article, we will get a full understanding of the vue slots through the practical application of its various use cases. Lets start with know about vuejs slots first.

What is Vue Slot?

Slots are reserved space offered by vuejs to display content passed down from one component to another. There are two types of the slot in vuejs namely: named slot and unnamed(default) slot.

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Practical Use Case of Vue Slots

• To pass down Html elements from one component to another.

With props, Vue allows us to pass strings, objects, arrays, and functions from a parent component to its child component. While it is possible for us to pass HTML elements from a parent to its child component as a string this will make our website vulnerable to cross-site scripting attack that is why vuejs provides us with a slot which is a more secure and reliable method of passing HTML element and other contents from parent to its child component for rendering.

HOW TO USE SLOT In the child component where the content is to be displayed, add the slot tag as follows:

In this tutorial, we will generate our project with the Vue CLI

vue create slot-project

Vue Template Slot

In the src folder create a components folder with parent.vue andchild.vue files

Adding the code below to child.vue

Add the code snippet below to parent.vue

Add the code snippet below to parent.vue

Here we imported the child component and pass down the HTML content to the child.

For these contents to be displayed in the child component, theslot tag must be added to the child component.

Lets add the slot tag to the child.vue file as follow:

In the app.js file add the parent.vue component

Now, we can verify that slot is working as expected.

Now our app should be like:

STYLING SLOT COMPONENT

For styling our slot component, the CSS styles should be added to the component with the slot tag.

So in child.vue component we will add the following styles to the HTML content received from the parent.vue component.

Using Multiple Slots

In order to use multiple slots in vue, vuejs provides us with away to name our slots.

Vue Slot Or Prop

What if we want the h2 and h3 tags in the parent component to be displayed individually in separate slots. This would be a typical use case for named slots.

In the Parent.vue component we will name our slots as follows:

In the child.vue component we will receive the named slot as follows:

Here vuejs reserves two slots to display the content of the slotattribute with the value of message and name as separate contents.

V Slot Vue

Conclusion

In this article, we have seen a practical use case of slots to transfer content from a parent component to a child component.

For more information on the slot, check out the Vue documentation.