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React css variables

React css variables

Learn Development at Frontend Masters. Frontend Masters has an in-depth course on Advanced CSS Layouts that digs into the big stuff like grid and flexbox, and then more like custom properties and calcusing them for advanced layouts and practical solutions.

Is it more powerful than setting directly the top and left style of an element? I see at least two advantages. One is the CSS readability: If you want to pin an element to the position of your cursor, left: var --mouse-x just makes total sense to me. Mixed with a few other CSS techniques this pretty much opens up for a whole lot of new opportunities. Yeas, I already use these powers evry day actually!

So great… until your client asks for IE compatibility. My question was more about performance : is it more performant to set a CSS variable than setting the top and left styles directly? Wanna learn modern CSS layout? Permalink to comment September 16, Matt Wood. Permalink to comment September 18, Permalink to comment September 24, Permalink to comment September 25, Anders Grimsrud. Permalink to comment October 1, This comment thread is closed.

If you have important information to share, please contact us.The plan for this article is to show you how native CSS variables work, and how you can use them to make your life a bit easier. As your web apps grow bigger, the CSS becomes big, redundant and many times messy. Used within a good context, the CSS variablesgive you the mechanism to reuse and easily change repeatedly occurring CSS properties.

But they required compiling before use, thus sometimesadding an extra layer of complexity. Let me start with something you may already be familiar with: using vars in JavaScript. To declare a simple JavaScript var you will write something like this:.

To declare a CSS variable you will have to add a double dash before the name of that var. Now, in order to use the value of the CSS variable, we can use the var … function. The easiest way to manage your CSS vars is by declaring them into the :root pseudo-class. Given the fact that the CSS variables follow the rules like any other CSS definition, having them in the :root will ensure that all selectors will gain access to these variables.

Both on mobile or desktop. Just be careful to provide a fallback if many of your users are still using IE. By far one of the best candidates for using CSS variables are the colors of your design. Instead of copy-and-pasting the same colors over and over again, we can just place them in variables.

Often you need to build a few different variants of components. Same base styles, just slightly different. The typical solution will be to create a base class, say. And now use them like this:. However, this will add some code duplication. On the. This can be easily fixed with a CSS variable.

CSS properties, like box-shadow, transform and font or other CSS rules with multiple parameters are perfect examples. We can place the property in a variable so that we can reuse it via a more human readable format. The standard cascade rules also apply to the CSS Variables. So, if a custom property is declared multiple times, the lowermost definition in the css file overwrites the ones above it.

The following example demonstrates how easy it is to dynamically manipulate properties on user action, while still keeping the code clear and concise.

react css variables

A great thing about CSS variables is their reactive nature. As soon as we update them, whatever property has the value of the CSS variable gets updated as well. So, with just a few lines of Javascript and the smart use of CSS Variables, we can make a theme switcher mechanism.This article arose out of a question about how to style React components.

There are various ways to style React Components.

react css variables

For example, I make use of notifications in React JS using Notyand the styling should be able to handle plugins too. There seems to be about eight different ways of styling React JS components used widely in the industry for production level work:.

There are a few restrictions like replacing every - with camelCase text. You can style them in two ways using JavaScript objects as shown in the example. The styles can be imported to any number of pages and elements unlike inline CSS, which is applied directly to the particular element. Normal CSS has several advantages, such as decreasing the file size with a clean code structure. You can maintain any number of style sheets, and it can be easier to change or customize styles when needed.

It can compile in the browser, on the server side or at build time in Node. It uses JavaScript as a language to describe styles in a declarative and maintainable way. When thinking in components, you no longer have to maintain a bunch of style sheets.

You can learn more about this approach in the JSS official documentation. You could normally create a React component along with the styles attached to it without having to create a separate file for CSS.

Styled-components allows us to create custom reusable components which can be less of a hassle to maintain. Props can be used in styling the components in the same way it is passed in the React components. Props are used instead of classes in CSS and set the properties dynamically.

Styled-components has a detailed documentation and the site also provides a live editor where you can try out the code. Get more information on styled components at styled-components: Basics. CSS Modules make sure that all of the styles for a component are at one single place and apply to that particular component.

This certainly solves the global scope problem of CSS. The composition feature acts as a weapon to represent shared styles between the states. The aim is to make the coding process simpler and more efficient.

Creating a Dark & Light Toggle Mode on your UI Designs

Just like other programming languages, Sass allows the use of variables, nesting, partials, imports and functions, which add super powers to regular CSS. Learn more about using and installing Sass with a variety of programming languages from their official documentation at Sass: Syntactically Awesome Style Sheets.

Less Leaner Style Sheets is a open-source, dynamic preprocessor style sheet language that can be compiled into CSS and run on the client side or server side.

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If there is a struggle in getting handy with styled components — as their syntax is slightly different from Normal CSS — this comes to the rescue. Stylable is just like CSS but offers more opportunities to make each component discreet. Along with the other properties of CSS, Stylable also offers custom pseudo classes and pseudo elements.

This property of Stylable automatically allows us to create custom CSS classes, which enables us to do the styling to internal parts of the components.Custom properties sometimes referred to as CSS variables or cascading variables are entities defined by CSS authors that contain specific values to be reused throughout a document.

They are set using custom property notation e. Complex websites have very large amounts of CSS, often with a lot of repeated values. For example, the same color might be used in hundreds of different places, requiring global search and replace if that color needs to change. An additional benefit is semantic identifiers.

For example, --main-text-color is easier to understand than 00ff00especially if this same color is also used in other contexts. Declaring a custom property is done using a custom property name that begins with a double hyphen --and a property value that can be any valid CSS value. Like any other property, this is written inside a ruleset, like so:. Note that the selector given to the ruleset defines the scope that the custom property can be used in.

A common best practice is to define custom properties on the element and is identical to the selector html, except that its specificity is higher. However, this doesn't always have to be the case: you maybe have a good reason for limiting the scope of your custom properties. Note : Custom property names are case sensitive — --my-color will be treated as a separate custom property to --My-color. As mentioned earlier, you use the custom property value by specifying your custom property name inside the var function, in place of a regular property value:.

Notice the repetition in the CSS.

CSS Variables

The background color is set to brown in several places. For some CSS declarations, it is possible to declare this higher in the cascade and let CSS inheritance solve this problem naturally. For non-trivial projects, this is not always possible. By declaring a custom property on the element and is identical to the selector html, except that its specificity is higher. This leads to the same result as the previous example, yet allows for one canonical declaration of the desired property value; very useful if you want to change the value across the entire page later.

Custom properties do inherit. This means that if no value is set for a custom property on a given element, the value of its parent is used. Take this HTML:. Keep in mind that these are custom properties, not actual variables like you might find in other programming languages. The value is computed where it is needed, not stored for use in other rules. For instance, you cannot set a property for an element and expect to retrieve it in a sibling's descendant's rule.

The property is only set for the matching selector and its descendants, like any normal CSS. Using the var function, you can define multiple fallback values when the given variable is not yet defined; this can be useful when working with Custom Elements and Shadow DOM. Fallback values aren't used to fix the browser compatibility.

If the browser doesn't support CSS custom Properties, the fallback value won't help. It's just a backup for the browser which supports CSS Custom Properties to choose a different value if the given variable isn't defined or has an invalid value.

The first argument to the function is the name of the custom property to be substituted. The second argument to the function, if provided, is a fallback value, which is used as the substitution value when the referenced custom property is invalid.

The function only accepts two parameters, assigning everything following the first comma as the second parameter. If that second parameter is invalid, such as if a comma-separated list is provided, the fallback will fail.

For example:. Including a custom property as a fallback, as seen in the second example above, is the correct way to provide more than one fallback. The technique has been seen to cause performance issues as it takes more time to parse through the variables.

Note : The syntax of the fallback, like that of custom propertiesallows commas. For example, var --foo, red, blue defines a fallback of red, blue — anything between the first comma and the end of the function is considered a fallback value.

The classical CSS concept of validity, tied to each property, is not very useful in regard to custom properties.I added an easter egg to my blog last week.

Adding Custom Environment Variables

We then promote it to its own composite layer using backface-visibility: hidden. This will mitigate any scrolling issues. We cannot see the color underneath. To fix this, we need to grayscale the image, invert the colors, and then add an opacity. We do all of this via CSS:.

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Looking good! Now it looks right! What can we do about that? The difference with CSS Variables is that they can be changed at runtime. Variables are always prepended with double-hyphens. Then we can change around the background color, and the linear-gradient using the var function. This means that we can change the any of these values individually. We can use an online color converter to convert from deepskyblue to HSLA.

We pass the event object into this method. For performance reasons, we only want the event listener to be active when the mouse button is actively being pressed. To do this, we set up handleMouseDown and handleMouseUp methods that will be called when the mousedown and mouseup events are triggered. We again pass the event object to the handleMouseDown method. We need to check if the initial click target which is e.

This is what verifies that the user initially clicked on the background before they started dragging their mouse. We use the element. We then pass in a selector. This blog uses Emotion JS to handle styling, so we have to pass in the same layoutStyles variable that we pass to Emotion.

A couple of notes here:.

Making Rainbows 🌈 with CSS Variables and React

Only if those selectors do not match, do we change the mousedown state and add an event listener for mousemove.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. If nothing happens, download GitHub Desktop and try again. If nothing happens, download Xcode and try again. If nothing happens, download the GitHub extension for Visual Studio and try again.

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The HOC won't trigger a render if only one of the variables is changed. This can be a huge performance improvement if you have a component with a deep render tree, since instead of passing props in elements as inline styles, you can only set variables, and no render will be triggered. Skip to content. Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together.

Sign up. A React component to set CSS variables. JavaScript Branch: master. Find file. Sign in Sign up. Go back. Launching Xcode If nothing happens, download Xcode and try again.

react css variables

Latest commit. Latest commit fc6b Mar 6, You signed in with another tab or window. Reload to refresh your session. You signed out in another tab or window.CSS variables are really cool. You can use them for a lot of things, like applying themes in your application with ease. In this tutorial I'll show you how to integrate them with React to create a ThemeComponent with context!

So first of all, I'd like to explain briefly what CSS variables or in their formal name - CSS custom properties are, and how to use them. CSS variables are a way for us to define variables that will be applied throughout our application.

The syntax is as follows:. What happens here? Does it seem really simple? That's because it is. There's not much to it. According to caniuse. So for the most part they're completely safe to use. If you want to read more, you can find more information in the MDN page. To get a value defined on an element:. Will give us the value of the primary custom CSS property defined for the element. The React Context API is the only way provided by React to pass props indirectly from one component to a descendent component.

In this guide I'll use the useContext hook, which you can read more about here.

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But the principle is the same with class components. The parameters passed to the React. Now that we have a context object, we can use it to "inject" props to our indirect descendants:.

Using CSS custom properties (variables)

No matter where in the component hierarchy our component lies, it has access to the themeName variable. If we want to allow editing the value in our context, we can pass a function like so:.

That's enough for our needs, but if you want you can further read on the Official React Context Documentation. Now that we know how to set CSS custom properties from JavaScript, and we can pass props down our component tree, we can make a really nice and simple "theme engine" for our application.

First up we'll define our themes:. This just happens to be the color pallette I use for my blog, but really the sky is the limit when it comes to themes, so feel free to experiment.

In this component we store our selected theme object, and the selected theme name, and we defined a function to toggle our selected theme. The last bit left is actually setting the CSS custom properties from our theme.

We can easily do it using the. Now for each value in our theme object we can access a CSS property with the same name prefixed with -- of course. The last thing we need is to run the setCSSVariables function every time the theme is toggled.

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So in our Theme component we can use the useEffect hook like so:. The full source code can be found on github. Clicking the Toggle will call the toggleTheme function, and will update our theme for the entire app, no more configuration needed. That's it! That's all you need to do to create a super simple, super clean theme engine for your application.

If you want to see a real live example, you can check out the source code of my blog. This article was previously published on my blog: dorshinar. If you want to read more content, you can check my blog as it would mean a lot to me. If you read this far, tweet to the author to show them you care.