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getInitialProps

Examples

getInitialProps enables server-side rendering in a page and allows you to do initial data population, it means sending the page with the data already populated from the server. This is especially useful for SEO.

getInitialProps will disable Automatic Static Optimization.

getInitialProps is an async function that can be added to any page as a static method. Take a look at the following example:

import fetch from 'isomorphic-unfetch'

function Page({ stars }) {
  return <div>Next stars: {stars}</div>
}

Page.getInitialProps = async ctx => {
  const res = await fetch('https://api.github.com/repos/zeit/next.js')
  const json = await res.json()
  return { stars: json.stargazers_count }
}

export default Page

Or using a class component:

import React from 'react'
import fetch from 'isomorphic-unfetch'

class Page extends React.Component {
  static async getInitialProps(ctx) {
    const res = await fetch('https://api.github.com/repos/zeit/next.js')
    const json = await res.json()
    return { stars: json.stargazers_count }
  }

  render() {
    return <div>Next stars: {this.props.stars}</div>
  }
}

export default Page

getInitialProps is used to asynchronously fetch some data, which then populates props.

Data returned from getInitialProps is serialized when server rendering, similar to what JSON.stringify does. Make sure the returned object from getInitialProps is a plain Object and not using Date, Map or Set.

For the initial page load, getInitialProps will execute on the server only. getInitialProps will only be executed on the client when navigating to a different route via the next/link component or by using next/router.

Context Object permalink

getInitialProps receives a single argument called context, it's an object with the following properties:

  • pathname - Current route. That is the path of the page in /pages
  • query - Query string section of URL parsed as an object
  • asPath - String of the actual path (including the query) shown in the browser
  • req - HTTP request object (server only)
  • res - HTTP response object (server only)
  • err - Error object if any error is encountered during the rendering

Caveats permalink

  • getInitialProps can not be used in children components, only in the default export of every page
  • If you are using server-side only modules inside getInitialProps, make sure to import them properly, otherwise it'll slow down your app

Related permalink

For more information on what to do next, we recommend the following sections: