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    Prevent CSS Class Name Collisions with Scoped Class Names in CSS-in-JS

    Oleg IsonenOleg Isonen

    Currently, CSS has no standardized and well-supported way to scope class names. By default, CSS selectors have one global namespace. This works fine as long as the code base is small, but when it grows and more than one person works on it, it becomes increasingly hard to manage selectors. This is the reason why many naming conventions like BEM, SMACSS, OOCSS have been created.

    We will learn how to make sure our class names have no collisions without using a naming convention. By doing this, we will have created our own minimalistic CSS-in-JS library.

    javascriptJavaScript
    cssCSS
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    Transcript

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    Instructor: 00:00 In order to avoid the class names conflicts, we can generate the class names. This key is not a class name anymore. It's a CSS rule name. In order to make sure our class names never have a collision, we will create a counter variable. We are going to increase this counter variable every time we create a class name. We will add this variable to the generated class name.

    00:23 Now we have to rename this key here as well because it's not a selector anymore. It's a rule name. We generate our selector using the name and the counter. We use the rule name inside of our selector in order to make it human readable. ++ will increment our counter so that we never have a collision. At the end, our selector will look like this.

    00:45 Let's have a look on the HTML of this button. The problem right now is that our button expects a class name CSS-in-JS minus button, but in reality our class name looks like this. We have to make our button use our new generated class name.

    01:01 Right now, we have our button rendered from index.html file. From now on, we are going to generate HTML from JavaScript. For simplicity reasons, we just use innerHTML on the body tag, and we use a template string.

    01:16 Somehow, we need to reference our generated class name from here. We need to rewrite our function in a way which allows us to access generated class names. Let's rename this function to CSS and the argument to styles.

    01:33 Previously, this function was returning a CSS string as a result. Now, we are going to return a classes object instead. Let's rename result to a CSS string. Let's return the classes object. Let's add to the classes object the generated class name. This way, we will be able to access our generated class name using our rule name.

    01:59 Here we just use our generated class name. Here we have to rename this object because we are using this name already. Let's call this object classes because this is what we're going to get there after we have called the CSS function.

    02:14 Now we have this error -- "CSS is not a function." The reason is we are calling this function before we have created this function. If we move this piece of code behind the declaration, this will start working.

    02:28 The next error is "To a CSS string is not defined." The reason is we've got to move this piece of logic to our CSS function. Now our CSS function is not only converting the object to a CSS string and generating the class name. It is also rendering the styles. As we now have an access to classes object, we can simply access the generated class name using the rule name.

    02:55 Let's have a quick look at the DOM. What we see is exactly what we have expected. It's using our generated class name. We can also have a look at the generated style tag, which looks something like this right now. We have basically created our own minimalistic CSS-in-JS library.

    03:14 Now I would like to move this CSS function to a separate module in order to make it reusable. Here is our CSS function in a separate module. Instead of defining a CSS function, we export a default function because it's our single export. Now our CSS button looks very tidy because we don't have this boilerplate anymore. We just import our CSS function from this CSS module.

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