Responsive Props in Vue Component - css

Question

I have a prop called src in a Vue Component that binds to a :style like this:
<template>
<section :class="color" class="hero" :style="{ backgroundImage: src && 'url(' + src + ')' }">
<slot></slot>
</section>
</template>
<script>
export default {
props: ['src', 'color']
}
</script>
What I would like to do is to create a list of responsive props that get used depending on the device or screen size of the site visitor.
For instance, I imagine a list of props like src-sm, src-md, src-lg, etc. The user would enter different image urls for different device sizes and the style attr would use the appropriate url depending on the screen/size.
Is this possible in VueJS. If so, any idea how?
Thanks.

Answer 1

Unfortuently what you are trying to do is not trivial. This is because inline style tags can not accept media queries.
The spec declares:
The value of the style attribute must match the syntax of the contents of a CSS declaration block
Solution 1:
This solution is the simplest, perhaps not entirely what you are looking for.
It works by including img elements, and showing an hiding them via CSS.
<template>
<div>
<img class="image--sm" :src="src.sm" />
<img class="image--md" :src="src.md" />
<img class="image--lg" :src="src.lg" />
</div>
</template>
<script>
export default {
props: {
src: Object
}
}
</script>
<style>
.image--md,
.image--lg {
display: none;
}
#media (min-width: 400px) {
.image--sm {
display: none;
}
.image--md {
display: block;
}
}
#media (min-width: 600px) {
.image--md {
display: none;
}
.image--lg {
display: block;
}
}
</style>
Example: https://jsfiddle.net/h3c5og08/1/
Solution 2:
Image tags may not be the desired effect you are trying to achieve. This solution creates a style tag in the head and injecting the css content to change the background images.
You can not have style tags in Vue template. It will throw an error like:
Templates should only be responsible for mapping the state to the UI. Avoid placing tags with side-effects in your templates, such as , as they will not be parsed.
As the error describes vue is designed the map state the UI. Using style tags in the template is prohibited because you can cause leaks to the outer world.
Although you can not declaratively styles in a template, we can use a bit of JS in the mounted hook of the component to add targetted and dynamic styles.
First we will need to constrain dynamic styles to this element. We can use the internal id of the created component this._uid, attaching to scope the css. (Note this is internal API so can be subject to change)
<template>
<div class="image" :data-style-scope="_uid">
</div>
</template>
The next part is to generate the style in a computed property, to later inject into a style block. You can expand on this computed property, to conditionaly assign properties ect. Note: keep the properties to the dynamic values only.
css () {
const selector = `.image[data-style-scope="${this._uid}"]`
const img = val => `${selector} { background-image: url("${val}"); }`
const sm = img(this.sm)
const md = img(this.md)
const lg = img(this.lg)
return `
${sm}
#media (min-width: 200px) { ${md} }
#media (min-width: 300px) { ${lg} }
`
}
This generated string from the css computed property is what we will now use when creating the style tag at mount. At mount we create a style node and append to the head. Assigning the nodes to the vm for references.
Using the references in the vm we can watch changes to the computed updating the style node.
Remember to clean up before destorying the component, removing the style node.
{
data () {
return {
// Reference data properties
style: null,
styleRef: null
}
},
mounted () {
// Create style node
let style = document.createElement('style')
style.type = "text/css"
style.appendChild(document.createTextNode(''))
// Assign references on vm
this.styleRef = style
this.style = style.childNodes[0]
// Assign css the the style node
this.style.textContent = this.css
// Append to the head
document.head.appendChild(style)
},
beforeDestroy () {
// Remove the style node from the head
this.style.parentElement.removeChild(this.style)
},
computed: {
css () {
// ...
}
},
watch: {
css (value) {
// On css value change update style content
this.style.textContent = this.css
}
}
}
Working Example: https://jsfiddle.net/bLkc51Lz/4/

Answer 2

You could also try the module described here: https://alligator.io/vuejs/vue-responsive-components/ which is called vue-responsive-components
It lets the component change its CSS depending on its own width (not on the entire browser's width)