Declan de Wet
Manage page meta info in Vue 2.0 components. SSR + Streaming supported. Inspired by react-helmet.
<template>
...
</template>
<script>
export default {
metaInfo: {
title: 'My Example App', // set a title
titleTemplate: '%s - Yay!', // title is now "My Example App - Yay!"
htmlAttrs: {
lang: 'en',
amp: undefined // "amp" has no value
}
}
}
</script>
Table of Contents
- Description
- Disclaimer
- Installation
- Usage
- Performance
- FAQ
Description
vue-meta is a Vue 2.0 plugin that allows you to manage your app's meta information, much like react-helmet does for React. However, instead of setting your data as props passed to a proprietary component, you simply export it as part of your component's data using the metaInfo property.
These properties, when set on a deeply nested component, will cleverly overwrite their parent components' metaInfo, thereby enabling custom info for each top-level view as well as coupling meta info directly to deeply nested subcomponents for more maintainable code.
Disclaimer
Please note that this project is still in very early alpha development and is not considered to be production ready. You have been warned. There is no sanitization yet, no tests, and you might even find some features are still missing.
Installation
Yarn
$ yarn add vue-meta
NPM
$ npm install vue-meta --save
CDN
Use the links below - if you want a previous version, check the instructions at https://unpkg.com.
Uncompressed:
<script src="https://unpkg.com/vue-meta@0.0.0/lib/vue-meta.js"></script>
Minified:
<script src="https://unpkg.com/vue-meta@0.0.0/lib/vue-meta.min.js"></script>
Usage
Step 1: Preparing the plugin
This step is optional if you don't need SSR and
Vueis available as a global variable.vue-metawill install itself in this case.
In order to use this plugin, you first need to pass it to Vue.use - if you're not rendering on the server-side, your JS entry file will suffice. If you are rendering on the server, then place it in a file that runs both on the server and on the client before your root instance is mounted. If you're using vue-router, then your main router.js file is a good place:
router.js:
import Vue from 'vue'
import Router from 'vue-router'
import Meta from 'vue-meta'
Vue.use(Router)
Vue.use(Meta)
export default new Router({
...
})
If you don't care about server-side rendering, you can skip straight to step 3. Otherwise, continue. 😄
Step 2: Server Rendering (Optional)
If you have an isomorphic/universal webapp, you'll likely want to render your metadata on the server side as well. Here's how.
Step 2.1: Exposing $meta to bundleRenderer
You'll need to expose the results of the $meta method that vue-meta adds to the Vue instance to the bundle render context before you can begin injecting your meta information. You'll need to do this in your server entry file:
server-entry.js:
import app from './app'
const router = app.$router
const meta = app.$meta() // here
export default (context) => {
router.push(context.url)
context.meta = meta // and here
return app
}
Step 2.2: Populating the document meta info with inject()
All that's left for you to do now before you can begin using metaInfo options in your components is to make sure they work on the server by inject-ing them so you can call text() on each item to render out the necessary info. You have two methods at your disposal:
Simple Rendering with renderToString()
Considerably the easiest method to wrap your head around is if your Vue server markup is rendered out as a string:
server.js:
app.get('*', (req, res) => {
const context = { url: req.url }
renderer.renderToString(context, (error, html) => {
if (error) return res.send(error.stack)
const {
title, htmlAttrs, bodyAttrs, link, style, script, noscript, meta
} = context.meta.inject()
return res.send(`
<!doctype html>
<html data-vue-meta-server-rendered ${htmlAttrs.text()}>
<head>
${meta.text()}
${title.text()}
${link.text()}
${style.text()}
${script.text()}
${noscript.text()}
</head>
<body ${bodyAttrs.text()}>
${html}
<script src="/assets/vendor.bundle.js"></script>
<script src="/assets/client.bundle.js"></script>
</body>
</html>
`)
})
})
Streaming Rendering with renderToStream()
A little more complex, but well worth it, is to instead stream your response. vue-meta supports streaming with no effort (on it's part 😜) thanks to Vue's clever bundleRenderer context injection:
server.js
app.get('*', (req, res) => {
const context = { url: req.url }
const renderStream = renderer.renderToStream(context)
renderStream.once('data', () => {
const {
title, htmlAttrs, bodyAttrs, link, style, script, noscript, meta
} = context.meta.inject()
res.write(`
<!doctype html>
<html data-vue-meta-server-rendered ${htmlAttrs.text()}>
<head>
${meta.text()}
${title.text()}
${link.text()}
${style.text()}
${script.text()}
${noscript.text()}
</head>
<body ${bodyAttrs.text()}>
`)
})
renderStream.on('data', (chunk) => {
res.write(chunk)
})
renderStream.on('end', () => {
res.end(`
<script src="/assets/vendor.bundle.js"></script>
<script src="/assets/client.bundle.js"></script>
</body>
</html>
`)
})
renderStream.on('error', (error) => res.status(500).end(`<pre>${error.stack}</pre>`))
})
Step 3: Start defining metaInfo
In any of your components, define a metaInfo property:
App.vue:
<template>
<div id="app">
<router-view></router-view>
</div>
</template>
<script>
export default {
name: 'App',
metaInfo: {
// if no subcomponents specify a metaInfo.title, this title will be used
title: 'Default Title',
// all titles will be injected into this template
titleTemplate: '%s | My Awesome Webapp'
}
}
</script>
Home.vue
<template>
<div id="page">
<h1>Home Page</h1>
</div>
</template>
<script>
export default {
name: 'Home',
metaInfo: {
title: 'My Awesome Webapp',
// override the parent template and just use the above title only
titleTemplate: null
}
}
</script>
About.vue
<template>
<div id="page">
<h1>About Page</h1>
</div>
</template>
<script>
export default {
name: 'About',
metaInfo: {
// title will be injected into parent titleTemplate
title: 'About Us'
}
}
</script>
Recognized metaInfo Properties
title (String)
Maps to the inner-text value of the <title> element.
{
metaInfo: {
title: 'Foo Bar'
}
}
<title>Foo Bar</title>
titleTemplate (String)
The value of title will be injected into the %s placeholder in titleTemplate before being rendered. The original title will be available on metaInfo.titleChunk.
{
metaInfo: {
title: 'Foo Bar',
titleTemplate: '%s - Baz'
}
}
<title>Foo Bar - Baz</title>
htmlAttrs (Object)
Each key:value maps to the equivalent attribute:value of the <html> element.
{
metaInfo: {
htmlAttrs: {
foo: 'bar',
amp: undefined
}
}
}
<html foo="bar" amp></title>
bodyAttrs (Object)
Each key:value maps to the equivalent attribute:value of the <body> element.
{
metaInfo: {
bodyAttrs: {
bar: 'baz'
}
}
}
<body bar="baz">Foo Bar</body>
base (Object)
Maps to a newly-created <base> element, where object properties map to attributes.
{
metaInfo: {
base: { target: '_blank', href: '/' }
}
}
<base target="_blank" href="/">
meta ([Object])
Each item in the array maps to a newly-created <meta> element, where object properties map to attributes.
{
metaInfo: {
meta: [
{ charset: 'utf-8' },
{ name: 'viewport', content: 'width=device-width, initial-scale=1' }
]
}
}
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
link ([Object])
Each item in the array maps to a newly-created <link> element, where object properties map to attributes.
{
metaInfo: {
link: [
{ rel: 'stylesheet', src: '/css/index.css' },
{ rel: 'favicon', src: 'favicon.ico' }
]
}
}
<link rel="stylesheet" src="/css/index.css">
<link rel="favicon" src="favicon.ico">
style ([Object])
Each item in the array maps to a newly-created <style> element, where object properties map to attributes.
{
metaInfo: {
style: [
{ cssText: '.foo { color: red }', type: 'text/css' }
]
}
}
<style type="text/css">.foo { color: red }</style>
script ([Object])
Each item in the array maps to a newly-created <script> element, where object properties map to attributes.
{
metaInfo: {
sript: [
{ innerHTML: '{ "@context": "http://schema.org" }', type: 'application/ld+json' }
]
}
}
<script type="application/ld+json">{ "@context": "http://schema.org" }</script>
noscript ([Object])
Each item in the array maps to a newly-created <noscript> element, where object properties map to attributes.
{
metaInfo: {
nosript: [
{ innerHTML: 'This website requires JavaScript.' }
]
}
}
<noscript>This website requires JavaScript.</noscript>
changed (Function)
Will be called when the client metaInfo updates/changes. Receives the following parameters:
newInfo(Object) - The new state of themetaInfoobject.addedTags([HTMLElement]) - a list of elements that were added.removedTags([HTMLElement]) - a list of elements that were removed.
this context is the component instance changed is defined on.
{
metaInfo: {
changed (newInfo, addedTags, removedTags) {
console.log('Meta info was updated!')
}
}
}
How metaInfo is Resolved
You can define a metaInfo property on any component in the tree. Child components that have metaInfo will recursively merge their metaInfo into the parent context, overwriting any duplicate properties. To better illustrate, consider this component heirarchy:
<parent>
<child></child>
</parent>
If both <parent> and <child> define a title property inside metaInfo, then the title that gets rendered will resolve to the title defined inside <child>.
Lists of Tags
When specifying an array in metaInfo, like in the below examples, the default behaviour is to simply concatenate the lists.
Input:
// parent component
{
metaInfo: {
meta: [
{ charset: 'utf-8' },
{ name: 'description', content: 'foo' }
]
}
}
// child component
{
metaInfo: {
meta: [
{ name: 'description', content: 'bar' }
]
}
}
Output:
<meta charset="utf-8">
<meta name="description" content="foo">
<meta name="description" content="bar">
This is not what we want, since the meta description needs to be unique for every page. If you want to change this behaviour such that description is instead replaced, then give it a vmid:
Input:
// parent component
{
metaInfo: {
meta: [
{ charset: 'utf-8' },
{ vmid: 'description', name: 'description', content: 'foo' }
]
}
}
// child component
{
metaInfo: {
meta: [
{ vmid: 'description', name: 'description', content: 'bar' }
]
}
}
Output:
<meta charset="utf-8">
<meta vmid="description" name="description" content="bar">
While solutions like react-helmet manage the occurrence order and merge behaviour for you automatically, it involves a lot more code and is therefore prone to failure in some edge-cases, whereas this method is almost bulletproof because of its versatility; at the expense of one tradeoff: these vmid properties will be rendered out in the final markup (vue-meta uses these client-side to prevent duplicating or overriding markup). If you are serving your content GZIP'ped, then the slight increase in HTTP payload size is negligible.
Performance
On the client, vue-meta batches DOM updates using requestAnimationFrame. It needs to do this because it registers a Vue mixin that subscribes to the beforeMount lifecycle hook on all components in order to be notified that renders have occurred and data is ready. If vue-meta did not batch updates, the DOM meta info would be re-calculated and re-updated for every component on the page in quick-succession.
Thanks to batch updating, the update will only occurr once - even if the correct meta info has already been compiled by the server. If you don't want this behaviour, see below.
How to prevent the update on the initial page render
Add the data-vue-meta-server-rendered attribute to the <html> tag on the server-side:
<html data-vue-meta-server-rendered>
...
vue-meta will check for this attribute whenever it attempts to update the DOM - if it exists, vue-meta will just remove it and perform no updates. If it does not exist, vue-meta will perform updates as usual.
Note: While this may seem verbose, it is intentional. Having
vue-metahandle this for you automatically would limit interoperability with other server-side programming languages. If you use PHP to power your server, for example, you might also have meta info handled on the server already and want to prevent this extraneous update.
FAQ
Here are some answers to some frequently asked questions.
How do I use component data in metaInfo?
Specify a function instead of an object. It will need to return the same type as its definition.
BlogPost.vue:
<template>
<div id="page">
<h1>{{ title }}</h1>
</div>
</template>
<script>
export default {
name: 'BlogPost',
data: () => ({
title: 'Sample blog post'
}),
metaInfo: {
title () {
return this.title
}
}
}
</script>
How do I use component props in metaInfo?
The same way you use data - specify a function instead of an object. It will need to return the same type as its definition.
BlogPostWrapper.vue
<template>
<div id="page">
<blog-post :title="title"></blog-post>
</div>
</template>
<script>
import BlogPost from './BlogPost.vue'
export default {
name: 'BlogPostWrapper',
components: { BlogPost },
data: () => ({
title: 'Example blog post'
})
}
</script>
BlogPost.vue
<template>
<div id="page">
<h1>{{ title }}</h1>
</div>
</template>
<script>
export default {
name: 'BlogPost',
props: ['title'],
metaInfo: {
title () {
return this.title
}
}
}
</script>