Creating and Modifying Pages

Gatsby makes it easy to programmatically control your pages.

Pages can be created in three ways:

In your site’s gatsby-node.js by implementing the API createPages
Gatsby core automatically turns React components in src/pages into pages
Plugins can also implement createPages and create pages for you

You can also implement the API onCreatePage to modify pages created in core or plugins or to create client-only routes.

Debugging help

To see what pages are being created by your code or plugins, you can query for page information while developing in GraphiQL. Paste the following query in the GraphiQL IDE for your site. The GraphiQL IDE is available when running your sites development server at HOST:PORT/___graphql e.g. localhost:8000/___graphql.

{
  allSitePage {
    edges {
      node {
        path
        component
        pluginCreator {
          name
          pluginFilepath
        }
      }
    }
  }
}

The context property accepts an object, and we can pass in any data we want the page to be able to access.

You can also query for any context data you or plugins added to pages.

NOTE: There are a few reserved names that cannot be used in context. They are: path, matchPath, component, componentChunkName, pluginCreator___NODE, and pluginCreatorId.

Creating pages in gatsby-node.js

Often you will need to programmatically create pages. For example, you have markdown files where each should be a page.

This example assumes that each markdown page has a path set in the frontmatter of the markdown file.

gatsby-node.js

// Implement the Gatsby API “createPages”. This is called once the
// data layer is bootstrapped to let plugins create pages from data.
exports.createPages = ({ graphql, actions }) => {
  const { createPage } = actions

  return new Promise((resolve, reject) => {
    const blogPostTemplate = path.resolve(`src/templates/blog-post.js`)
    // Query for markdown nodes to use in creating pages.
    resolve(
      graphql(
        `
          {
            allMarkdownRemark(limit: 1000) {
              edges {
                node {
                  frontmatter {
                    path
                  }
                }
              }
            }
          }
        `
      ).then(result => {
        if (result.errors) {
          reject(result.errors)
        }

        // Create pages for each markdown file.
        result.data.allMarkdownRemark.edges.forEach(({ node }) => {
          const path = node.frontmatter.path
          createPage({
            path,
            component: blogPostTemplate,
            // In your blog post template's graphql query, you can use path
            // as a GraphQL variable to query for data from the markdown file.
            context: {
              path,
            },
          })
        })
      })
    )
  })
}

Modifying pages created by core or plugins

Gatsby core and plugins can automatically create pages for you. Sometimes the default isn’t quite what you want and you need to modify the created page objects.

Removing trailing slashes

A common reason for needing to modify automatically created pages is to remove trailing slashes.

To do this, in your site’s gatsby-node.js add code similar to the following:

Note: There’s also a plugin that will remove all trailing slashes from pages automatically: gatsby-plugin-remove-trailing-slashes.

Note: If you need to perform an asynchronous action within onCreatePage you can return a promise or use an async function.

gatsby-node.js

// Replacing '/' would result in empty string which is invalid
const replacePath = path => (path === `/` ? path : path.replace(/\/$/, ``))
// Implement the Gatsby API “onCreatePage”. This is
// called after every page is created.
exports.onCreatePage = ({ page, actions }) => {
  const { createPage, deletePage } = actions

  const oldPage = Object.assign({}, page)
  // Remove trailing slash unless page is /
  page.path = replacePath(page.path)
  if (page.path !== oldPage.path) {
    // Replace new page with old page
    deletePage(oldPage)
    createPage(page)
  }
}

Pass context to pages

The automatically created pages can receive context and use that as variables in their GraphQL queries. To override the default and pass your own context, open your site’s gatsby-node.js and add similar to the following:

gatsby-node.js

exports.onCreatePage = ({ page, actions }) => {
  const { createPage, deletePage } = actions

  deletePage(page)
  // You can access the variable "house" in your page queries now
  createPage({
    ...page,
    context: {
      ...page.context,
      house: `Gryffindor`,
    },
  })
}

On your pages and templates, you can access your context via the prop pageContext like this:

import React from "react"

const Page = ({ pageContext }) => {
  return <div>{pageContext.house}</div>
}

export default Page

Page context is serialized before being passed to pages: This means it can’t be used to pass functions into components.

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