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vue-server-renderer

server renderer for Vue 2.0

vue-server-renderer

This package is auto-generated. For pull requests please see src/entries/web-server-renderer.js.

This package offers Node.js server-side rendering for Vue 2.0.

Installation

npm install vue-server-renderer

API

createRenderer([rendererOptions])

Create a renderer instance.

const renderer = require('vue-server-renderer').createRenderer()

renderer.renderToString(vm, cb)

Render a Vue instance to string. The callback is a standard Node.js callback that receives the error as the first argument:

const Vue = require('vue')
 
const renderer = require('vue-server-renderer').createRenderer()
 
const vm = new Vue({
  render (h) {
    return h('div', 'hello')
  }
})
 
renderer.renderToString(vm, (err, html) => {
  console.log(html) // -> <div server-rendered="true">hello</div> 
})

renderer.renderToStream(vm)

Render a Vue instance in streaming mode. Returns a Node.js readable stream.

// example usage with express 
app.get('/', (req, res) => {
  const vm = new App({ url: req.url })
  const stream = renderer.renderToStream(vm)
 
  res.write(`<!DOCTYPE html><html><head><title>...</title></head><body>`)
 
  stream.on('data', chunk => {
    res.write(chunk)
  })
 
  stream.on('end', () => {
    res.end('</body></html>')
  })
})

createBundleRenderer(code, [rendererOptions])

Creates a bundleRenderer instance using pre-bundled application code (see Creating the Server Bundle). For each render call, the code will be re-run in a new context using Node.js' vm module. This ensures your application state is discrete between requests, and you don't need to worry about structuring your application in a limiting pattern just for the sake of SSR.

const bundleRenderer = require('vue-server-renderer').createBundleRenderer(code)

bundleRenderer.renderToString([context], cb)

Render the bundled app to a string. Same callback interface with renderer.renderToString. The optional context object will be passed to the bundle's exported function.

bundleRenderer.renderToString({ url: '/' }, (err, html) => {
  // ... 
})

bundleRenderer.renderToStream([context])

Render the bundled app to a stream. Same stream interface with renderer.renderToStream. The optional context object will be passed to the bundle's exported function.

bundleRenderer
  .renderToStream({ url: '/' })
  .pipe(writableStream)

Renderer Options

directives

Allows you to provide server-side implementations for your custom directives:

const renderer = createRenderer({
  directives: {
    example (vnode, directiveMeta) {
      // transform vnode based on directive binding metadata 
    }
  }
})

As an example, check out v-show's server-side implementation.


cache

Provide a component cache implementation. The cache object must implement the following interface:

{
  get: (key: string, [cb: Function]) => string | void,
  set: (key: string, val: string) => void,
  has?: (key: string, [cb: Function]) => boolean | void // optional 
}

A typical usage is passing in an lru-cache:

const LRU = require('lru-cache')
 
const renderer = createRenderer({
  cache: LRU({
    max: 10000
  })
})

Note that the cache object should at least implement get and set. In addition, get and has can be optionally async if they accept a second argument as callback. This allows the cache to make use of async APIs, e.g. a redis client:

const renderer = createRenderer({
  cache: {
    get: (key, cb) => {
      redisClient.get(key, (err, res) => {
        // handle error if any 
        cb(res)
      })
    },
    set: (key, val) => {
      redisClient.set(key, val)
    }
  }
})

Why Use bundleRenderer?

In a typical Node.js app, the server is a long-running process. If we directly require our application code, the instantiated modules will be shared across every request. This imposes some inconvenient restrictions to the application structure: we will have to avoid any use of global stateful singletons (e.g. the store), otherwise state mutations caused by one request will affect the result of the next.

Instead, it's more straightforward to run our app "fresh" for each request, so that we don't have to think about avoiding state contamination across requests. This is exactly what bundleRenderer helps us achieve.

Creating the Server Bundle

screen shot 2016-08-11 at 6 06 57 pm

The application bundle can be generated by any build tool, so you can easily use Webpack + vue-loader with the bundleRenderer. You do need to use a slightly different webpack config and entry point for your server-side bundle, but the difference is rather minimal:

  1. add target: 'node', and use output: { libraryTarget: 'commonjs2' } for your webpack config. Also, it's probably a good idea to externalize your dependencies.

  2. In your server-side entry point, export a function. The function will receive the render context object (passed to bundleRenderer.renderToString or bundleRenderer.renderToStream), and should return a Promise, which should eventually resolve to the app's root Vue instance:

// server-entry.js 
import Vue from 'vue'
import App from './App.vue'
 
const app = new Vue(App)
 
// the default export should be a function 
// which will receive the context of the render call 
export default context => {
  // data pre-fetching 
  return app.fetchServerData(context.url).then(() => {
    return app
  })
}

Externals

When using the bundleRenderer, we will by default bundle every dependency of our app into the server bundle as well. This means on each request these depdencies will need to be parsed and evaluated again, which is unnecessary in most cases.

We can optimize this by externalizing dependencies from your bundle. During the render, any raw require() calls found in the bundle will return the actual Node module from your rendering process. With Webpack, we can simply list the modules we want to externalize using the externals config option:

// webpack.config.js 
module.exports = {
  // this will externalize all modules listed under "dependencies" 
  // in your package.json 
  externals: Object.keys(require('./package.json').dependencies)
}

Externals Caveats

Since externalized modules will be shared across every request, you need to make sure that the dependency is idempotent. That is, using it across different requests should always yield the same result - it cannot have global state that may be changed by your application. Interactions between externalized modules are fine (e.g. using a Vue plugin).

Component Caching

You can easily cache components during SSR by implementing the serverCacheKey function:

export default {
  name: 'item', // required 
  props: ['item'],
  serverCacheKey: props => props.item.id,
  render (h) {
    return h('div', this.item.id)
  }
}

Note that cachable component must also define a unique "name" option. This is necessary for Vue to determine the identity of the component when using the bundle renderer.

With a unique name, the cache key is thus per-component: you don't need to worry about two components returning the same key. A cache key should contain sufficient information to represent the shape of the render result. The above is a good implementation if the render result is solely determined by props.item.id. However, if the item with the same id may change over time, or if render result also relies on another prop, then you need to modify your getCacheKey implementation to take those other variables into account.

Returning a constant will cause the component to always be cached, which is good for purely static components.

When to use component caching

If the renderer hits a cache for a component during render, it will directly reuse the cached result for the entire sub tree. So do not cache a component containing child components that rely on global state.

In most cases, you shouldn't and don't need to cache single-instance components. The most common type of components that need caching are ones in big lists. Since these components are usually driven by objects in database collections, they can make use of a simple caching strategy: generate their cache keys using their unique id plus the last updated timestamp:

serverCacheKey: props => props.item.id + '::' + props.item.last_updated

Client Side Hydration

In server-rendered output, the root element will have the server-rendered="true" attribute. On the client, when you mount a Vue instance to an element with this attribute, it will attempt to "hydrate" the existing DOM instead of creating new DOM nodes.

In development mode, Vue will assert the client-side generated virtual DOM tree matches the DOM structure rendered from the server. If there is a mismatch, it will bail hydration, discard existing DOM and render from scratch. In production mode, this assertion is disabled for maximum performance.

Hydration Caveats

One thing to be aware of when using SSR + client hydration is some special HTML structures that may be altered by the browser. For example, when you write this in a Vue template:

<table>
  <tr><td>hi</td></tr>
</table>

The browser will automatically inject <tbody> inside <table>, however, the virtual DOM generated by Vue does not contain <tbody>, so it will cause a mismatch. To ensure correct matching, make sure to write valid HTML in your templates.