gatsby-node.js

const path = require('path')

exports.onCreateNode = ({ node, boundActionCreators, getNode }) => {
  const { createNodeField } = boundActionCreators
  let slug
  if (node.internal.type === `MarkdownRemark` || node.internal.type === `JSFrontmatter`) {
    const fileNode = getNode(node.parent)
    const parsedFilePath = path.parse(fileNode.relativePath)
    if (parsedFilePath.name !== `index` && parsedFilePath.dir !== ``) {
      slug = `/${parsedFilePath.dir}/${parsedFilePath.name}/`
    } else if (parsedFilePath.dir === ``) {
      slug = `/${parsedFilePath.name}/`
    } else {
      slug = `/${parsedFilePath.dir}/`
    }

    // Add slug as a field on the node.
    createNodeField({ node, name: `slug`, value: slug })
  }
}

exports.createPages = ({ graphql, boundActionCreators }) => {
  const { createPage } = boundActionCreators

  return new Promise((resolve, reject) => {
    const pages = []
    const markdownTemplate = path.resolve("src/templates/markdown.js")
    const jsTemplate = path.resolve("src/templates/javascript.js")

    // Query for all markdown "nodes" and for the slug we previously created.
    resolve(
      graphql(
      `
        {
          allMarkdownRemark {
            edges {
              node {
                frontmatter {
                  layoutType
                  path
                }
                fields {
                  slug
                }
              }
            }
          }
          allJsFrontmatter {
            edges {
              node {
                fileAbsolutePath
                data {
                  layoutType
                  path
                }
                fields {
                  slug
                }
              }
            }
          }
        }
      `
      ).then(result => {
        if (result.errors) {
          console.log(result.errors)
          console.log(result)
          reject(result.errors)
        }

        // Create from markdown
        result.data.allMarkdownRemark.edges.forEach(edge => {
            let frontmatter = edge.node.frontmatter;
            // ideally we would want to use layoutType to
            //  decide which (nested) layout to use, but
            //  gatsby currently doesnt support this.
            if (frontmatter.layoutType === 'post' ||
                frontmatter.layoutType === 'page') {
                createPage({
                  path: frontmatter.path, // required
                  component: markdownTemplate,
                  context: {
                    layoutType: frontmatter.layoutType,
                    slug: edge.node.fields.slug,
                  },
                })
            }
        })

        // Create pages from javascript
        // Gatsby will, by default, createPages for javascript in the
        //  /pages directory. We purposely don't have a folder with this name
        //  so that we can go full manual mode.
        result.data.allJsFrontmatter.edges.forEach(edge => {
            let frontmatter = edge.node.data;
            // see above
            if (frontmatter.layoutType === 'post' ||
                frontmatter.layoutType === 'page') {
                createPage({
                  path: frontmatter.path, // required
                  // Note, we can't have a template, but rather require the file directly.
                  //  Templates are for converting non-react into react. jsFrontmatter
                  //  picks up all of the javascript files. We have only written these in react.
                  component: path.resolve(edge.node.fileAbsolutePath),
                  context: {
                    layoutType: frontmatter.layoutType,
                    slug: edge.node.fields.slug,
                  },
                })
              } else if (edge.node.fields.slug === '/index/') {
                createPage({
                  path: '/', // required, we don't have frontmatter for this page hence separate if()
                  component: path.resolve(edge.node.fileAbsolutePath),
                  context: {
                    slug: edge.node.fields.slug,
                  },
                })
              }
        })

        return
      })
    )
  })
}