Putting Things in Context With React

Context is currently an experimental API for React – but soon to be a first class citizen! There are a lot of reasons it is interesting but perhaps the most is that it allows for parent components to pass data implicitly to their children, no matter how deep the component tree is. In other words, data can be added to a parent component and then any child can tap into it.

See the Pen React Context Lights by Neal Fennimore (@nealfennimore) on CodePen.

While this is often the use case for using something like Redux, it’s nice to use if you do not need complex data management. Think about that! We create a custom downstream of data, deciding which props are passed and at which levels. Pretty cool.

Context is great in areas of where you have a lot of components that depend on a single piece of data, but are deep within the component tree. Explicitly passing each prop to each individual component can often be overwhelming and it is a lot easier just to use context here.

For example, let’s consider how we would normally pass props down the tree. In this case, we’re passing the color red using props on each component in order to move it on down the stream.

class Parent extends React.Component { render(){ return <Child color="red" />; }
} class Child extends React.Component { render(){ return <GrandChild color={this.props.color} /> }
} class GrandChild extends React.Component { render(){ return ( <div style={{color: this.props.color}}> Yep, I'm the GrandChild </div> ); }

What if we never wanted the Child component to have the prop in the first place? Context saves us having to go through the Child component with color and pass it directly from the Parent to the GrandChild:

class Parent extends React.Component { // Allow children to use context getChildContext() { return { color: 'red' }; } render(){ return <Child />; }
} Parent.childContextTypes = { color: PropTypes.string
}; class Child extends React.Component { render() { // Props is removed and context flows through to GrandChild return <GrandChild /> }
} class GrandChild extends React.Component { render() { return ( <div style={{color: this.context.color}}> Yep, I'm still the GrandChild </div> ); }
} // Expose color to the GrandChild
GrandChild.contextTypes = { color: PropTypes.string

While slightly more verbose, the upside is exposing the color anywhere down in the component tree. Well, sometimes…

There’s Some Gotchas

You can’t always have your cake and eat it too, and context in it’s current form is no exception. There are a few underlying issues that you’ll more than likely come into contact with if you end up using context for all but the simplest cases.

Context is great for being used on an initial render. Updating context on the fly? Not so much. A common issue with context is that context changes are not always reflected in a component.

Let’s dissect these gotchas in more detail.

Gotcha 1: Using Pure Components

Context is hard when using PureComponent since by default it does not perform any shallow diffing by default with context. Shallow diffing with PureComponent is testing for whether the values of the object are strictly equal. If they’re not, then (and only then) will the component update. But since context is not checked, well… nothing happens.

See the Pen React Context Lights with PureComponents by Neal Fennimore (@nealfennimore) on CodePen.

Gotcha 2: Should Component Update? Maybe.

Context also does not update if a component’s shouldComponentUpdate returns false. If you have a custom shouldComponentUpdate method, then you’ll also need to take context into consideration. To enable updates with context, we could update each individual component with a custom shouldComponentUpdate that looks something like this.

import shallowEqual from 'fbjs/lib/shallowEqual'; class ComponentThatNeedsColorContext extends React.PureComponent { // nextContext will show color as soon as we apply ComponentThatNeedsColorContext.contextTypes // NOTE: Doing the below will show a console error come react v16.1.1 shouldComponentUpdate(nextProps, nextState, nextContext){ return !shallowEqual(this.props, nextProps) || !shallowEqual(this.state, nextState) || !shallowEqual(this.context, nextContext); }
} ComponentThatNeedsColorContext.contextTypes = { color: PropTypes.string

However, this does not solve the issue of an intermediary PureComponent between the parent and the child blocking context updates. This means that every PureComponent between the parent and child would need to have contextTypes defined on it, and they would also need to have an updated shouldComponentUpdate method. And at this point, that’s a lot of work for very little gain.

Better Approaches to the Gotchas

Fortunately, we have some ways to work around the gotchas.

Approach 1: Use a Higher Order Component

A Higher Order Component can read from context and pass the needed values on to the next component as a prop.

import React from 'react'; const withColor = (WrappedComponent) => { class ColorHOC extends React.Component { render() { const { color } = this.context; return <WrappedComponent style={{color: color}} {...this.props} /> } } ColorHOC.contextTypes = { color: React.PropTypes.string }; return ColorHOC;
}; export const Button = (props)=> <button {...props}>Button</button> // ColoredButton will render with whatever color is currently in context with a style prop
export const ColoredButton = withColor( Button );

See the Pen React Context Lights with HOC by Neal Fennimore (@nealfennimore) on CodePen.

Approach 2: Use Render Props

Render Props allow us to use props to share code between two components.

class App extends React.Component { getChildContext() { return { color: 'red' } } render() { return <Button /> }
} App.childContextTypes = { color: React.PropTypes.string
} // Hook 'Color' into 'App' context
class Color extends React.Component { render() { return this.props.render(this.context.color); }
} Color.contextTypes = { color: React.PropTypes.string
} class Button extends React.Component { render() { return ( <button type="button"> {/* Return colored text within Button */} <Color render={ color => ( <Text color={color} text="Button Text" /> ) } /> </button> ) }
} class Text extends React.Component { render(){ return (  {this.props.text}  ) }
} Text.propTypes = { text: React.PropTypes.string, color: React.PropTypes.string,

Approach 3: Dependency Injection

A third way we can work around these gotchas is to use Dependency Injection to limit the context API and allow components to subscribe as needed.

The New Context

The new way of using context, which is currently slated for the next minor release of React (16.3), has the benefits of being more readable and easier to write without the “gotchas” from previous versions. We now have a new method called createContext, which defines a new context and returns both a Provider and Consumer.

The Provider establishes a context that all sub-components can hook into. It’s hooked in via Consumer which uses a render prop. The first argument of that render prop function, is the value which we have given to the Provider. By updating the value within the Provider, all consumers will update to reflect the new value.

As a side benefit with using the new context, we no longer have to use childContextTypes, getChildContext, and contextTypes.

const ColorContext = React.createContext('color');
class ColorProvider extends React.Component { render(){ return ( <ColorContext.Provider value={'red'}> { this.props.children } </ColorContext.Provider> ) }
} class Parent extends React.Component { render(){ // Wrap 'Child' with our color provider return ( <ColorProvider> <Child /> </ColorProvider> ); }
} class Child extends React.Component { render(){ return <GrandChild /> }
} class GrandChild extends React.Component { render(){ // Consume our context and pass the color into the style attribute return ( <ColorContext.Consumer> {/* 'color' is the value from our Provider */} { color => ( <div style={{color: color}}> Yep, I'm still the GrandChild </div> ) } </ColorContext.Consumer> ); }

Separate Contexts

Since we have more granular control in how we expose context and to what components are allowed to use it, we can individually wrap components with different contexts, even if they live within the same component. We can see this in the next example, whereby using the LightProvider twice, we can give two components a separate context.

See the Pen React Context Lights with new Context by Neal Fennimore (@nealfennimore) on CodePen.


Context is a powerful API, but it’s also very easy to use incorrectly. There are also a few caveats to using it, and it can be very hard to figure out issues when components go awry. While Higher-Order Components and dependency injection offer alternatives for most cases, context can be used beneficially in isolated portions of your code base.

With the next context though, we no longer have to worry about the gotchas we had with the previous version. It removes having to define contextTypes on individual components and opens up the potential for defining new contexts in a reusable manner.

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Going From Dumb Little Idea to Real Website in Like 10 Minutes

I live in Bend, Oregon. I woke up with the dumbest idea ever that there should be a little food truck map website and it should be called Vend, Oregon. It’s not my finest idea, but hey, I’m full of those. Fortunately, we don’t have to spend all day on this.

1) Figure out what’s going to go on this dumb little website

Fortunately, all the hard work was already done. One of our local rags already created a list of them. They allude to a map multiple times, but it’s hard to dig it up. In searching around a bit, I found this which does have an embedded Google Map.

Perhaps this can be useful then! Let’s blow up this map and embed it properly!

2) Make the dumb site

Fortunately, Google Maps are embeddable. Let’s just slap their embed code in an HTML document:

<body> <iframe src="https://www.google.com/maps/d/embed?mid=1bg2tr60F_w395jAY-WW8JGbwSCM" width="640" height="480"></iframe>

And have it cover the entire page:

html, body { margin: 0; height: 100%; overflow: hidden;
} iframe { postion: absolute; top: 0; left: 0; width: 100%; height: 100%; border: 0;

Let’s use CodePen Projects for this, as that’ll get us another step closer to having this live.

The extra files there are just a Bend logo I fired through RealFaviconGenerator.

3) Buy the dumb domain name

This is the point where you really start to question the idea. But, go ahead and pull the trigger anyway. The internet needs you.

4) It’s dumb, but it it might as well be HTTPS

One big reason to use CloudFlare is you get HTTPS even on their free plan. Might as well take advantage of that. This means pointing the nameservers from your domain registrant over to CloudFlare.

5) Deploy the CodePen Project

You can deploy the site right out of CodePen Projects.

Note that you get some IP addresses there. Add those as A Records right in CloudFlare and you’re done!

6) Bask in your dumb idea

Swear to god, 10 minutes from start to finish.

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The Vue Cookbook

I’m extremely excited to announce that the Vue Cookbook is officially in beta! For the past few months, the Vue team has been writing, and editing and accepting PRs from the community to build a new section of our docs called the Cookbook. Each recipe stands on its own, meaning that recipes can focus on one specific aspect of Vue or something that integrates with Vue, and do a small deep dive into that subject. We can then include more complex examples, combining features in interesting ways.

One of my favorite parts of the cookbook is the Alternative Patterns section of each recipe. Usually when people write blog posts or document something, they’re also selling you on the concept that they’re explaining. In the cookbook, we strive to consider that we’re all building different kinds of applications and websites, and thus a variety of choices will be valid, given divergent scenarios. The cookbook spends a little time in each recipe weighing the tradeoffs, and considering when one might need another path.

For advanced features, we assume some ecosystem knowledge. For example, if you want to use single-file components in Webpack, we don’t explain how to configure the non-Vue parts of the Webpack config. In the cookbook, we have the space to explore these ecosystem libraries in more depth—at least to the extent that is universally useful for Vue developers.

This section will continue to be in development! We have more recipes that we’re writing, we’re still accepting PRs, and the more community involvement, the richer a resource it becomes! I hope you enjoy it and find it useful.

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React State From the Ground Up

As you begin to learn React, you will be faced with understanding what state is. State is hugely important in React, and perhaps a big reason you’ve looked into using React in the first place. Let’s take a stab at understanding what state is and how it works.

What is State?

State, in React, is a plain JavaScript object that allows you keep track of a component’s data. The state of a component can change. A change to the state of a component depends on the functionality of the application. Changes can be based on user response, new messages from server-side, network response, or anything.

Component state is expected to be private to the component and controlled by the same component. To make changes to a component’s state, you have to make them inside the component — the initialization and updating of the component’s state.

Class Components

States is only available to components that are called class components. The main reason why you will want to use class components over their counterpart, functional components, is that class components can have state. Let’s see the difference. Functional components are JavaScript functions, like this:

const App = (props) => { return ( <div> { this.props } </div> )

If the functionality you need from your component is as simple as the one above, then a functional component is the perfect fit. A class component will look a lot more complex than that.

class App extends React.Component { constructor(props) { super(props) this.state = { username: 'johndoe' } } render() { const { username } = this.state return( <div> { username } </div> ) }

Above, I am setting the state of the component’s username to a string.

The Constructor

According to the official documentation, the constructor is the right place to initialize state. Initializing state is done by setting this.state to an object, like you can see above. Remember: state is a plain JavaScript object. The initial state of the App component has been set to a state object which contains the key username, and its value johndoe using this.state = { username: 'johndoe' }.

Initializing a component state can get as complex as what you can see here:

constructor(props) { super(props) this.state = { currentTime: 0, status: false, btnOne: false, todoList: [], name: 'John Doe' }

Accessing State

An initialized state can be accessed in the render() method, as I did above.

render() { const { username } = this.state return( <div> { username } </div> )

An alternative to the above snippet is:

render() { return( <div> { this.state.username } </div> )

The difference is that I extracted the username from state in the first example, but it can also be written as const status = this.state.username. Thanks to ES6 destructuring, I do not have to go that route. Do not get confused when you see things like this. It is important to know that I am not reassigning state when I did that. The initial setup of state was done in the constructor, and should not be done again – never update your component state directly.

A state can be accessed using this.state.property-name. Do not forget that aside from the point where you initialized your state, the next time you are to make use of this.state is when you want to access the state.

Updating State

The only permissible way to update a component’s state is by using setState(). Let’s see how this works practically.

First, I will start with creating the method that gets called to update the component’s username. This method should receive an argument, and it is expected to use that argument to update the state.

handleInputChange(username) { this.setState({username})

Once again, you can see that I am passing in an object to setState(). With that done, I will need to pass this function to the event handler that gets called when the value of an input box is changed. The event handler will give the context of the event that was triggered which makes it possible to obtain the value entered in the input box using event.target.value. This is the argument passed to handleInputChange() method. So, the render method should look like this.

render() { const { username } = this.state return ( <div> <div> <input type="text" value={this.state.username} onChange={event => this.handleInputChange(event.target.value)} /> </div> <p>Your username is, {username}</p> </div> )

Each time setState() is called, a request is sent to React to update the DOM using the newly updated state. Having this mindset makes you understand that state update can be delayed.

Your component should look like this;

class App extends React.Component { constructor(props) { super(props) this.state = { username: 'johndoe' } } handleInputChange(username) { this.setState({username}) } render() { const { username } = this.state return ( <div> <div> <input type="text" value={this.state.username} onChange={event => this.handleInputChange(event.target.value)} /> </div> <p>Your username is, {username}</p> </div> ) }

Passing State as Props

A state can be passed as props from a parent to the child component. To see this in action, let’s create a new component for creating a To Do List. This component will have an input field to enter daily tasks and the tasks will be passed as props to the child component.

Try to create the parent component on your own, using the lessons you have learned thus far.

Let’s start with creating the initial state of the component.

class App extends React.Component { constructor(props) { super(props) this.state = { todoList: [] } } render() { return() }

The component’s state has its todoList set to an empty array. In the render() method, I want to return a form for submitting tasks.

render() { const { todoList } = this.state return ( <div> <h2>Enter your to-do</h2> <form onSubmit={this.handleSubmit}> <label>Todo Item</label> <input type="text" name="todoitem" /> <button type="submit">Submit</button> </form> </div > )

Each time a new item is entered and the submit button is clicked, the method handleSubmit gets called. This method will be used to update the state of the component. The way I want to update it is by using concat to add the new value in the todoList array. Doing so will set the value for todoList inside the setState() method. Here’s how that should look:

handleSubmit = (event) => { event.preventDefault() const value = (event.target.elements.todoitem.value) this.setState(({todoList}) => ({ todoList: todoList.concat(value) }))

The event context is obtained each time the submit button is clicked. We use event.preventDefault() to stop the default action of submission which would reload the page. The value entered in the input field is assigned a variable called value, which is then passed an argument when todoList.concat() is called. React updates the state of todoList by adding the new value to the initial empty array. This new array becomes the current state of todoList. When another item is added, the cycle repeats.

A chart illustrating the cycle explained above.

The goal here is to pass the individual item to a child component as props. For this tutorial, we’ll call it the TodoItem component. Add the code snippet below inside the parent div which you have in render() method.

<div> <h2>Your todo lists include:</h2> { todoList.map(i => <TodoItem item={i} /> )}

You’re using map to loop through the todoList array, which means the individual item is then passed to the TodoItem component as props. To make use of this, you need to have a TodoItem component that receives props and renders it on the DOM. I will show you how to do this using functional and class components.

Written as a functional component:

const TodoItem = (props) => { return ( <div> {props.item} </div> )

For the class component, it would be:

class TodoItem extends React.Component { constructor(props) { super(props) } render() { const {item} = this.props return ( <div> {item} </div> ) }

If there is no need to manage state in this component, you are better off using functional component.

Leveling Up

You will be handling state very often while developing React application. With all the areas covered above, you should have the confidence of being able to dive into the advanced part of state management in React. To dig deeper, I recommend React’s official documentation on State and Lifecycle as well as Uber’s React Guide on Props vs State.

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Microsoft Edge Variable Fonts Demo

The Edge team put together a thorough demo of variable fonts, showcasing them in all of their shape-shifting and adaptive glory. Equally interesting as the demo itself is a history of web typography and where variable fonts fit in the grand scheme of things.

This demo pairs well with v-fonts.com, which is an interactive collection of variable fonts that allows you to play around with the variable features each font provides.

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A simple resource for finding and trying variable fonts

This is a website designed to showcase fonts that support OpenType Variations and let you drag a whole bunch of sliders around to manipulate a typeface’s width, height, and any other settings that the type designer might’ve added to the design.

I think the striking thing about this project is that I had no idea just how many variable fonts were out there in the wild until now.

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Theming With Variables: Globals and Locals

Cliff Pyles contributed to this post.

Setting CSS variables to theme a design system can be tricky: if they are too scoped, the system will lose consistency. If they are too global, you lose granularity.

Maybe we can fix both issues. I’d like to try to boil design system variables down to two types: Global and Component variables. Global variables will give us consistency across components. Component variables will give us granularity and isolation. Let me show you how to do it by taking a fairly simple component as an example.

Heads up, I’ll be using CSS variables for this article but the concept applies to preprocessor variables as well.

Global-scoped variables

System-wide variables are general concepts defined to keep consistency across your components.

Starting with an .alert component as an example, let’s say we want to keep consistency for all of our spaces on margins and paddings. We can first define global spacers:

:root { --spacer-sm: .5rem; --spacer-md: 1rem; --spacer-lg: 2rem;

And then use on our components:

/* Defines the btn component */
.btn { padding: var(--spacer-sm) var(--spacer-md);
} /* Defines the alert component */
.alert { padding: var(--spacer-sm) var(--spacer-md);

The main benefits of this approach are:

  • It generates a single source of truth for spacers, and a single point for the author using our system to customize it.
  • It achieves consistency since every component follows the same spacing.
  • It produces a common point of reference for designers and developers to work from. As long as the designers follow the same spacing restrictions, the translation to code is seamless.

But it also presents a few problems:

  • The system loses modularity by generating a dependency tree. Since components depend on global variables, they are no longer isolated.
  • It doesn’t allow authors to customize a single component without overwriting the CSS. For example, to change the padding of the alert without generating a system wide shift, they’d have to overwrite the alert component:
.alert { padding-left: 1rem; padding-right: 1rem;

Chris Coyier explains the idea of theming with global variables using custom elements in this article.

Component-scoped variables

As Robin Rendle explain in his article, component variables are scoped to each module. If we generate the alert with these variables, we’d get:

.alert { --alert-color: #222; color: var(--alert-color); border-color: var(--alert-color);

The main advantages are:

  • It creates a modular system with isolated components.
  • Authors get granular control over components without overwriting them. They’d just redefine the value of the variable.

There is no way to keep consistency across components or to make a system wide change following this method.

Let’s see how we can get the best of both worlds!

The two-tier theming system

The solution is a two-layer theming system where global variables always inform component variables. Each one of those layers follow a set of very specific rules.

First tier: Global variables

The main reason to have global variables is to maintain consistency, and they adhere to these rules:

  • They are prefixed with the word global and follow the formula --global--concept--modifier--state--PropertyCamelCase
    • a concept is something like a spacer or main-title
    • a state is something like hover, or expanded
    • a modifier is something like sm, or lg
    • and a PropertyCamelCase is something like BackgroundColor or FontSize
  • They are concepts, never tied to an element or component
    • this is wrong: --global-h1-font-size
    • this is right: --global--main-title--FontSize

For example, a global variable setup would look like:

:root { /* --global--concept--size */ --global--spacer--sm: .5rem; --global--spacer--md: 1rem; --global--spacer--lg: 2rem; /* --global--concept--PropertyCamelCase */ --global--main-title--FontSize: 2rem; --global--secondary-title--FontSize: 1.8rem; --global--body--FontSize: 1rem; /* --global--state--PropertyCamelCase */ --global--hover--BackgroundColor: #ccc;

Second tier: Component variables

The second layer is scoped to theme-able component properties and follow these rules:

  • Assuming we are writing BEM, they follow this formula: --block__element--modifier--state--PropertyCamelCase
    • The block__element--modifier the selector name is something like alert__actions or alert--primary
    • a state is something like hover or active
    • and if you are not writing BEM class names the same principles apply, just replace the block__element--modifier with your classname
  • The value of component scoped variables is always defined by a global variable
  • A component variable always has a default value as a fallback in case the component doesn’t have the dependency on the global variables

For example:

.alert { /* Component scoped variables are always defined by global variables */ --alert--Padding: var(--global--spacer--md); --alert--primary--BackgroundColor: var(--global--primary-color); --alert__title--FontSize: var(--global--secondary-title--FontSize); /* --block--PropertyCamelCase */ padding: var(--alert--Padding, 1rem); /* Sets the fallback to 1rem. */
} /* --block--state--PropertyCamelCase */
.alert--primary { background-color: var(--alert--primary--BackgroundColor, #ccc);
} /* --block__element--PropertyCamelCase */
.alert__title { font-size: var(--alert__title--FontSize, 1.8rem);

You’ll notice that we are defining locally-scoped variables with global variables. This is key for the system to work since it allows authors to theme the system as a whole. For example, if they want to change the primary color across all components they just need to redefine --global--primary-color.

On the other hand each component variable has a default value so a component can stand on its own, it doesn’t depend on anything and authors can use it in isolation.

This setup allows for consistency across components, it generates a common language between designers and developers since we can set the same global variables in Sketch as bumpers for designers, and it gives granular control to authors.

Why does this system work?

In an ideal world, we as creators of a design system, expect “authors” or users of our system to implement it without modifications, but of course, the world is not ideal and that never happens.

If we allow authors to easily theme the system without having to overwrite CSS, we’ll not only make their lives easier but also reduce the risk of breaking modules. At the end of the day, a maintainable system is a good system.

The two-tier theming system generates modular and isolated components where authors have the possibility to customize them at a global and at a component level. For example:

:root { /* Changes the secondary title size across the system */ --global--secondary-title--FontSize: 2rem;
} .alert { /* Changes the padding on the alert only */ --alert--Padding: 3rem;

What values should became variables?

CSS variables open windows to the code. The more we allow authors in, the more vulnerable the system is to implementation issues.

To keep consistency, set global variables for everything except layout values; you wouldn’t want authors to break the layout. And as a general rule, I’d recommend allowing access to components for everything you are willing to give support.

For the next version of PatternFly, an open source design system I work on, we’ll allow customization for almost everything that’s not layout related: colors, spacer, typography treatment, shadows, etc.

Putting everything together

To show this concept in action I’ve created a CodePen project:

Global variables are nestled in _global-variables.scss. They are the base to keep consistency across the system and will allow the author to make global changes.

There are two components: alert and button. They are isolated and modular entities with scoped variables that allow authors to fine tune components.

Remember that authors will use our system as a dependency in their project. By letting them modify the look and feel of the system through CSS variables, we are creating a solid code base that’s easier to maintain for the creators of the system and better to implement, modify, and upgrade to authors using the system.

For example, if an author wants to:

  • change the primary color to pink across the system;
  • change the danger color to orange just on the buttons;
  • and change the padding left to 2.3rem only on the alert…

…then this is how it’s done:

:root { // Changes the primary color on both the alert and the button --global--primary--Color: hotpink;
} .button { // Changes the danger color on the button only without affecting the alert --button--danger--BackgroundColor: orange; --button--danger--hover--BorderColor: darkgoldenrod;
} .alert { // Changes the padding left on the alert only without affecting the button --alert--PaddingLeft: 2.3rem;

The design system code base is intact and it’s just a better dependency to have.

I am aware that this is just one way to do it and I am sure there are other ways to successfully set up variables on a system. Please let me know what you think on the comments or send me a tweet. I’d love to hear about what you are doing and learn from it.

The post Theming With Variables: Globals and Locals appeared first on CSS-Tricks.

Building A Static Site With Components Using Nunjucks

We’re so used to either a backend language or a JavaScript framework powering our data-backed components. I love me a Rails partial with a bunch of locals: {} or a <Component ...props /> but you don’t have to give up on components even if working in static HTML. With Nunjucks, which has includes and templates and macros, we have a robust toolset for building component-based sites that are easy, fast, and secure to host.

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Animate a Container on Mouse Over Using Perspective and Transform

I’ve been working on a website in which large pictures are displayed to the user. Instead of creating a typical lightbox effect (a zoom-in animation with a black overlay) for these large pictures, I decided to try and make something more interactive and fun. I ended up coding an image container that tilts as the user moves the mouse cursor above it.

Here’s the final version:

See the Pen MrLopq by Mihai (@MihaiIonescu) on CodePen.

This effect is achieved through CSS and JavaScript. I figured I’d make a little tutorial explaining how each part works so you could easily reproduce it or extend it.

I recommend reading up on the almanac entries for perspective and transform before we get started. We’re going to refer to these properties through the post and it’s a good idea to be familiar with them.

Let’s get down to it.


First, we need a container with another inner element. The container will help with the perspective.

<div id="container"> <div id="inner"></div>

For demonstration purposes, let’s center the card exactly in the middle of the screen:

body { /* Full screen width and height */ width: 100%; min-height: 100vh; /* Centers the container in the middle of the screen */ display: flex; justify-content: center; align-items: center; margin: 0; background-color: rgb(220, 220, 220);
} #container { /* This will come into play later */ perspective: 40px;
} #inner { width: 20em; height: 18em; background-color: white;

This gives us a white card that is positioned directly in the center of a light gray background. Note that we’ve set the perspective of the #container to 40px which does nothing at this point because we have not created any transforms. That will be handled later in the JavaScript.

See the Pen 3D Image Container – Part 0 by Mihai (@MihaiIonescu) on CodePen.

Let’s Start Scripting

Here’s the outline for what we’re doing:

var container = document.getElementById('container');
var inner = document.getElementById('inner'); var onMouseEnterHandler = function(event) { update(event);
var onMouseLeaveHandler = function() { inner.style = "";
var onMouseMoveHandler = function(event) { if (isTimeToUpdate()) { update(event); }
}; container.onmouseenter = onMouseEnterHandler;
container.onmouseleave = onMouseLeaveHandler;
container.onmousemove = onMouseMoveHandler;

And here is what all those things are (or will) be doing:

  • Handler Functions: these functions handle the events as they happen. We want to decide what happens when the cursor enters, moves over, and leaves the container, so each of those has a handler.
  • Update Function: We haven’t coded this yet but its goal will be to update the 3D rotation of our #inner div.
  • Time to Update Function: This is another function we haven’t coded yet but it will return true when an update is required. This is a way to reduce the number of calls to the update() function and improve the performance of our script.
  • Event: This is a JavaScript object that describes the event that occurred.

The code above will:

  • Update the 3D rotation of the inner div as soon as the mouse enters the container.
  • Update the 3D rotation of the inner div when the appropriate time comes as the mouse moves over the container.
  • Reset the style of the inner div when the mouse leaves the container.

Is it Time to Update?

Let’s add the function that decides when to update the 3D rotation of the #inner div.

var counter = 0;
var updateRate = 10;
var isTimeToUpdate = function() { return counter++ % updateRate === 0;

When the counter reaches the updateRate, an update will be made.

At this point, you can try replacing the update function by a console.log() and play with the updateRate to see how it all works together.

The Mouse

Next up is the mouse object. This one is a little more complex than the other sections. Still, it’s not that difficult to understand, but the code can seem intimidating, especially if you’re new to JavaScript.

// Init
var container = document.getElementById('container');
var inner = document.getElementById('inner');
// Mouse var mouse = { _x: 0, _y: 0, x: 0, y: 0, updatePosition: function(event) { var e = event || window.event; this.x = e.clientX - this._x; this.y = (e.clientY - this._y) * -1; }, setOrigin: function(e) { this._x = e.offsetLeft + Math.floor(e.offsetWidth/2); this._y = e.offsetTop + Math.floor(e.offsetHeight/2); }, show: function() { return '(' + this.x + ', ' + this.y + ')'; }
// Track the mouse position relative to the center of the container.

Again, let’s walk through this together.

  • show(): Displays the current position of the mouse (if you want to do some debugging in the browser’s console).
  • setOrigin(e): Sets the coordinates (0,0) of our mouse object at the center of the element (e).
  • updatePosition(): Updates the current position of our mouse object, relative to (0,0).

The last line of code mouse.setOrigin(container) snaps the coordinates (0,0) of our mouse object to the center of our container. Here’s an example that illustrates it.

See the Pen 3D Image Container – Part 1 by Mihai (@MihaiIonescu) on CodePen.

The idea behind all this is to add more rotation to our #inner div as you move the mouse farther from the center of the container.

Update Styles on Mouse Position

Here’s our update function:

var update = function(event) { mouse.updatePosition(event); updateTransformStyle( (mouse.y / inner.offsetHeight/2).toFixed(2), (mouse.x / inner.offsetWidth/2).toFixed(2) );
}; var updateTransformStyle = function(x, y) { var style = "rotateX(" + x + "deg) rotateY(" + y + "deg)"; inner.style.transform = style; inner.style.webkitTransform = style; inner.style.mozTransform = style; inner.style.msTransform = style; inner.style.oTransform = style;
  • update(): Updates the mouse position and updates the style of the #inner div.
  • updateTransformStyle(): Updates the style for each vendor prefix.

Are We Done?

We’d better do some testing! Looks like we get a change in perspective when the mouse cursor enters and exits the card, but it’s not as smooth as it could be:

See the Pen 3D Image Container – Part 2 by Mihai (@MihaiIonescu) on CodePen.

Oh right! We told it to update the rotation of our #inner div every time the counter hits the updateRate. This produces a clunky transition between updates.

How do we solve that? CSS transitions.

Adding Transitions

#inner { transition: transform 0.5s;

These are arbitrary numbers. You can play with the perspective and transform values to make the effect more or less dramatic as you see fit.

See the Pen 3D Image Container – Part 3 by Mihai (@MihaiIonescu) on CodePen.

Note that resizing the page will cause some problems because the position of the container changes in the page. The solution is to re-center your mouse object in your container after the page is resized.

Wrapping Up

We’re done! Now we have a container for making an element a little more interactive. The demo at the beginning of this post uses an image inside of the container, but this can be used for other things besides images, including forms, modals, or just about any other content you drop in the container. Go experiment!

The post Animate a Container on Mouse Over Using Perspective and Transform appeared first on CSS-Tricks.

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