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⚠️ This project is no longer maintained ⚠️

Many of the features in Second are now available in the core React library, and as such Second will no longer be maintained. Thanks so much for your support!

Read the blog post

Second is a framework for building and rendering React components on the server. It provides a higher-order data component that enables UI components to declare their data dependencies. Second ensures that all data dependencies are met before completing a render cycle. Components that require interactivity in the browser can be dehydrated with their original props, and rehydrated in the browser.

In traditional rock climbing, the second is the climber that ascends after the lead climber has placed protection on the route and created an anchor at the top. Seconding is typically much easier and safer than leading.

Second consists of several components:

  • second-container - Higher-order component that enables UI components to declare their data dependencies. Integrates with second-fetcher to ensure components are only rendered once their data requirements have been met.
  • second-fetcher - Interprets and fulfils data requirements.
  • second-renderer - A lightweight wrapper around any VDOM library that implements createElement(), renderToString(), and optionally renderToStaticMarkup(). Can be integrated with second-fetcher to ensure all data requirements are met before completing the render cycle.
  • second-dehydrator - Dehydrates a component's props and state so that it can be selectively rehydrated on the client.
  • second-bundler - Experimental runtime stylesheet bundler.


npm install --save second

Getting started

Make sure you first install a VDOM library with a React-compatible API. For example, install React with npm install --save react react-dom.

const VDom = require('react')
const VDomServer = require('react-dom/server')
const second = require('second')

second.init({ VDom, VDomServer })

const Component = require('./your-react-component')
const props = {}

second.render(Component, props).then(content =>
  console.log('Output:', content)

Use the higher-order container component to declare data requirements:

// your-react-component.js
const React = require('react')
const second = require('second')

const WrappedComponent = require('./other-component')

module.exports = second.createContainer(WrappedComponent, {
  data: (props) => ({
    // Each key is provided to the wrapped component as a prop
    repo: {
      // Use props to programmatically fetch data
      uri: `${props.repoName}`,

      // Optionally extract only the response properties that you need, to reduce
      // the amount of data that is sent to the browser
      pick: ['name', 'url', 'stargazers_count']

    contributors: {
      uri: `${props.repoName}/contributors`

Dehydrate components to prepare them for rehydration on the client:

// sub-component.js
const React = require('react')
const second = require('second')

class SubComponent extends React.Component {
  render () {
    // ...

module.exports = second.dehydrate(SubComponent)

// main-component.js
const React = require('react')
const SubComponent = require('./sub-component')

module.exports = class MainComponent extends React.Component {
  render () {
    return (
        <SubComponent prop1="foo" prop2="bar">
          <span>Children will be dehydrated as well!</span>

Example application

For a more complete example of a Second application, see example-simple-api.



git clone
npm install
npm run lerna bootstrap

Running the example application

Run the example API server with

npm start

Second understands the NODE_ENV and DEBUG environment variables:

NODE_ENV=production DEBUG=second:* npm start

Running the tests

Run the tests during development with:

npm run lerna run test

Or if you have Lerna installed globally:

lerna run test