Themes in React.js (for Vietnam friends)

Xin chào

My name is Thomas. People usually call me TOM. I have worked as a web developer for more than 16 years in Korea and I really enjoy programming. that is why I love open source as well. I have created and operated several open source projects.
Today, I would like to talk about Themes in React.
I’ve been developing with jQuery for over 10 years and built many websites and libraries.

But now I’ve fallen even more in love with React.

There are many reasons why I love React. But today I’d like to share the top two reasons:

First, React makes developing enjoyable and using JSX is fun. Specially…Hot Module Replacement is the best function to use. With the HRM, you can save a lot of time as you can run your application without refreshing. You also can exchange, add and remove modules while the app is running.

The second reason is, the great UI components made with React make it possible to develop quickly.

They can be found at NPM easily which speeds up development, and there are heaps more useful components.

Using JSX and Styled Components.

Let ’s look at how to develop using JSX and Styled Components.

For example, If you don’t use ‘Styled Components’,. Then you need to enter ‘className’ in the node when you do styling. So… to create or modify a ‘CSS Class’, you will need to open the CSS file.

But usually what happened?! You already have so many files opened on your screen, and it looks horrible to open another one, is that right?

Or you can add the ‘style’ property in the next line, but it generally ends up looking messy.

We think it is better to avoid complicating the body of the render function, don’t you agree?

Then how about we just use ‘Styled Components’?

Create a ‘Styled’ function that can be used directly in JSX with the Styled-Component syntax and use it according to the JSX syntax in the render.

And If you use ‘VSCode’ also you can use a ‘styled-component’ plugin which “autocomplete” the CSS

if you have a Styled-Component that needs to be re-used or needs to be redefined, you can define it in a separate file and export it.

In my case, image assets are also made into styled components. Usually, each image is defined in a different style, but then it allows you to manage image assets efficiently.

Like this, you can import the exported components to the specific location that you want and use JSX in your render. It’s very simple and easy to follow.

I like to code semantically in the render with no attributes unless it is really necessary.

Awesome ecosystem

The State of JavaScript Frameworks, 2017

This is a graph from the NPM annual report in 2017. As you can see React is growing rapidly every year, and have beaten all the other framework.

You can get almost all the components free for your development if you use React. Creating UI for sites like these components by yourself can be very time-consuming. But if you install NPM. you can use these components to your projects as you just import them.

I think the reason why so many great components are available is that of the well-made life cycle of the React and JSX.



And I am also making and distributing some of React components. One of my components is datagrid. Datagrid is designed to print only parts of data that are represented in tables. This way you can print, scroll, and modify the data very quickly.

Thank you so much! because you will click the Star Button on my project.

Ant Design

Ok back to React. One of the most powerful UI frameworks in recent years is Ant Design. I have tried Bootstrap, Materialize and Semantic UI. But Ant is the most enjoyable to use so far. Here are a few reasons why:

First, it’s made of React and Typescript.

Second, the variety of components available and its excellent features make it easy to create complex and large web applications.

Third, Ant Design has no problem with using styled components. Style components are not usually available for components that don’t support className props.

Fourth, it is well documented and has many examples.

And last, it has more than thirty-four thousand stars on Github.


Now let’s get to the main point of today’s presentation.

If you’re a front-end developer working on a web application, you might be thinking about how to create a theme. Because themes are hard to make and even harder to maintain.

As I mentioned earlier, I like to use Styled Components and Ant. To manage Themes using these two, you need to use “LESS” to change the theme for Ant. and use the “ThemeProvider” for Styled Components.

So if you want to change the “primaryColor” value, you must change both the “theme.less” file and the “theme.ts” files. Even if you don’t use AntD, you will have similar issues when you are using Styled Components on other frameworks.

So how can you change the primaryColor value at once?

It will be the main problem if you work in a team with others. I’ve tried many ways to solve the issue, but today I want to share 3 of them with you.

The first try was using the LESS file.

In the CSS module loader, you can use the export selector in the LESS file. The CSS-module allows variables in export to be used as variables in JS. In this example, defined primary_color and info_color.

Then import the LESS file as a theme variable. After that…creating ‘styled’ and ‘ThemeProvider’ according to the Styled Component theme guide.

Wrap it with a ThemeProvider that has theme props.

Now you can use the theme variable when you use styled on a component.

To summarize, in the file ‘antd-theme.less’, the exported theme to ‘ThemeProvider’ from ‘styledComponents’.

So the components that are wrapped in the ThemeProvider can use the value of the theme. And there is nothing to change in Ant Design, right?

The advantage of this way is you can use the color value from the Theme variable value as a function of LESS. For example, you can use color functions such as lighten, darken, and fade-in of LESS.

But there is a problem with it. IDE doesn’t support auto-completion. Because it doesn’t know the type of the theme that I brought from the LESS file. (To resolve this issue, you must create a d.ts file of the LESS file. I tried to create a d.ts. file every time the LESS file was changed, but it wasn’t smooth.)

I could still use it as is, but I wasn’t satisfied with it as I use Typescript. So I tried something else.

So the second try was building a LESS file with a TS file.

First, make a “theme.ts” file. And create a theme object and add primary_color and info_color keys. Then export.

This time make the ‘theme.ts’ file as a theme variable. And do the same way to create a ThemeProvider.

If you see this picture. You create a “theme.ts” file and when you update it, the “theme-vars.less” file is also updated. So styled-components uses the “theme.ts file” as the theme, and Ant uses the “theme-vars.less file” as the theme.

The hardest part is how to watch files.

So I decided to use a node. Define the source path to the TS file and the target path to the LESS file.

Next, Create a function called “buildLessVar” In the function, read the “theme.ts” file and replace it with a dash from underscore to create the file.

Use ‘watchFile’ in the “nodeJS” to run the “buildLessVar” function whenever the “theme.ts” file updated.

Then create a script to run the “package.json” file when NPM starts. We used “ts-node” since we have a TS file.

So if you enter the “NPM start” command into the terminal, “build-watch” and “WEBPACK services” will be running simultaneously and go on standby.

This is what it looks like when the “theme-vars.less” file is created. Once you import from “index.less”, the theme for Ant is resolved.

And see. Now you can use AutoComplete with Styled Components.

Not only is “autocomplete” available, but TypeScript also gives a notification when the developer accidentally uses the wrong variable name.

That means you wouldn’t make any mistakes. How convenient, isn’t it?

Ok, then let’s take a look at the demo.

Please note that the source code for this demo in more detail can be found below link.

Enter the “NPM start” command in the terminal to start the server. Let’s open the “theme.ts” file and change the value of primary_color. As you can see, the color of all the controls has changed.

If you look closely, you will see the color of the title differs from the label color of a Form control. And the text-color on the bottom is inverted according to the background color.

To allow color representation to be detailed, we used the color function from the “npm plugin” to modify the color values defined in the theme.

Because the way of the color function is a little longer, it would be cleaner to make it simple like in the second line.

Finally, the text at the bottom of the page is inverted by determining if the background color is a Dark color.

This will allow any color to respond to the background color.

For the last way, I am going to show creating a theme using only CSS.

Make the variable in the theme into CSS custom properties. You can create a color variable using a keyword in :root selector.

Then use the “VAR” function where it’s needed. You can use this feature with any modern browsers except Internet Explorer.

As you can see, did CSS override for Ant.

Earlier, we used a function to modify the color values. The problem will be solved if you use the “color-mod” that is defined to CSS4 spec.

However, none of the browsers are supporting this feature yet. But it’s only a matter of time before we can use this feature because it’s rapidly being developed.

Ok then….let’s look at a demo of a theme that was created this way.

Open the Chrome console and let’s change the color. It’s still challenging to use this technology, but I expect it to be sooner to be used.

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