Reading Server Data & :global Classes

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We just set a global currentCategoryId variable in JavaScript. Let's use this in our Vue app to highlight which category we're currently viewing.

Open up sidebar.vue. How can we get the current category info here? The simplest way is... to reference the global variable! We will talk soon about ways to organize this, but since we created a global variable in Twig, we can absolutely use that here!

Well... we can't use it immediately in our Vue template. If we tried to use currentCategoryId to add a dynamic class, Vue would think that we were trying to reference this.currentCategoryId.

We have two options. First, we could add a currentCategoryId data and initialize it to window.currentCategoryId. That would be fine. But because I don't intend for this value to change while my Vue app is running - at least not yet - it doesn't really need to live as data, though it wouldn't hurt anything,

Instead, let's leverage a computed property... which is a great way to expose any extra variables you need in a template.

Below data, add computed and create a new computed property called currentCategoryId. Inside, return window.currentCategoryId.

... lines 1 - 42
<script>
... lines 44 - 45
export default {
... lines 47 - 58
computed: {
currentCategoryId() {
return window.currentCategoryId;
},
},
... lines 64 - 68
};
</script>
... lines 71 - 85

It's just that simple!

Adding the .selected Style

Before we use this in the template, let's add a new class that we can use for the "selected" category. Inside the ul, create a new style called li a.selected. This is the class that we will need to dynamically add in the template. Inside, say background: $light-dash-component-border;.

... lines 1 - 77
<style lang="scss" module>
... lines 79 - 80
.component {
... lines 82 - 83
ul {
... lines 85 - 88
li a.selected {
background: $light-component-border;
}
}
}
</style>

This comes indirectly from the light-component mixin we're using - it's actually a variable set in colors.scss.

Ok! Let's use this selected class up in the template. Start with the "all products" item: this should have the selected class if the currentCategoryId is null. And it should always have the nav-link class.

To do that, change this to :class and set it to an object. Inside, add a key called nav-link set true so that it always shows up. For the dynamic class, add [$style.selected] - to reference our new selected class - and make that render if currentCategoryId === null.

<template>
... lines 2 - 8
<li class="nav-item">
<a
:class="{
'nav-link': true,
[$style.selected]: currentCategoryId === null,
}"
... line 15
>All Products</a>
</li>
... lines 18 - 46
</template>
... lines 48 - 95

Remember: the ugly square bracket syntax is needed so that JavaScript knows that our key is a dynamic expression. That's... unfortunate, but we're going to fix that in a minute anyways!

Now copy the :class attribute and, down inside the loop, paste over the existing class. In this case, we want to show the class if category['@id'] === currentCategoryId.

<template>
... lines 2 - 18
<li
v-for="category in categories"
... lines 21 - 22
>
<a
... line 25
:class="{
'nav-link': true,
[$style.selected]: category['@id'] === currentCategoryId,
}"
>
{{ category.name }}
</a>
</li>
... lines 34 - 46
</template>
... lines 48 - 95

Testing time! Back on the browser... yes! It already works! I'm on the "Office Supplies" page and that category is highlighted! Let's click on "All Products" and... it works beautifully!

So even though we don't have access to the global variable directly in our template, it's very simple to create a computed property that grabs that for us and makes it available!

SASS Globals

There's one thing I want to improve before we talk about a better way to manage global variables.

It bothers me a little bit that I have to use $style.selected... especially because I'm forced to use the ugly [] syntax! If you look down at our CSS, we're already inside of a modular .component class. On the top of our template: yep! We're using $style.component on the root element.

In SASS, because I put the .selected class inside of .component, the style will only apply to elements that are inside the root element.

Move over to your browser and "inspect element" on the selected link. Not surprisingly, this has a modular selected class: sidebar_selected_ and then a dynamic hash. But check out how the CSS is generated for this: it's .sidebar_component_ a hash and then ul li.sidebar_selected_ and another hash! We don't actually need that second hash! The first .sidebar_component_ hash selector is already enough to make sure that our selected class doesn't affect anything else on the page.

So here's what I would love to be able to do: I want to be able to write CSS like we're doing now - but not have any classes inside .component render in a modular way. Up in the template, I want to be able to just type selected and have it work.

<template>
... lines 2 - 9
<a
:class="{
... line 12
'selected': currentCategoryId === null,
}"
... line 15
>All Products</a>
... lines 17 - 46
</template>
... lines 48 - 95

Make our child style classes into globals

And here's how: down in the style tag, you can tell SCSS:

Hey! I'm using a selected class, but I don't want you to treat this like a modular class: I don't want you to add the prefix and hash.

The way you do that is by adding :global in front of it.

... lines 1 - 77
<style lang="scss" module>
... lines 79 - 80
.component {
... lines 82 - 83
ul {
... lines 85 - 88
:global li a.selected {
... line 90
}
}
}
</style>

As soon as we do that, if I inspect element on the selected link and look at the generated CSS selector on the right... yes! It has the modular sidebar class but then it only says .selected. We're not worried about that affecting any other parts of the page because it's still inside the modular sidebar class.

And... we can go one step further! If you think about it, because .component will be converted into a modular class, we don't need any classes inside of it to be modular. We can move the :global up and after the .component class.

... lines 1 - 80
.component :global {
... lines 82 - 83
ul {
... lines 85 - 88
li a.selected {
... line 90
}
}
}
... lines 94 - 95

Now everything inside will not be modular. This means that the only time I should have to use the $style variable is on the root element! The rest can be normal classes. This already looks much better!

Next, we have successfully referenced a global variable via a computed property. But I don't love having global variables hidden inside my code. We can do this in a better, more organized way, by refactoring it into a service!

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This course is also built to work with Vue 3!

What JavaScript libraries does this tutorial use?

// package.json
{
    "devDependencies": {
        "@symfony/webpack-encore": "^0.30.0", // 0.30.2
        "axios": "^0.19.2", // 0.19.2
        "bootstrap": "^4.4.1", // 4.5.0
        "core-js": "^3.0.0", // 3.6.5
        "eslint": "^6.7.2", // 6.8.0
        "eslint-config-airbnb-base": "^14.0.0", // 14.1.0
        "eslint-plugin-import": "^2.19.1", // 2.20.2
        "eslint-plugin-vue": "^6.0.1", // 6.2.2
        "regenerator-runtime": "^0.13.2", // 0.13.5
        "sass": "^1.29.0", // 1.29.0
        "sass-loader": "^8.0.0", // 8.0.2
        "vue": "^2.6.11", // 2.6.11
        "vue-loader": "^15.9.1", // 15.9.2
        "vue-template-compiler": "^2.6.11", // 2.6.11
        "webpack-notifier": "^1.6.0" // 1.8.0
    }
}