gatsby-node.js

const { createFilePath } = require(`gatsby-source-filesystem`)
const path = require(`path`)

exports.onCreateNode = ({ node, getNode, boundActionCreators }) => {
  const { createNodeField } = boundActionCreators
  if (node.internal.type === `MarkdownRemark`) {
    const slug = createFilePath({ node, getNode, basePath: `pages` })
    createNodeField({
      node,
      name: `slug`,
      value: slug,
    })
  }
}

exports.createPages = ({ graphql, boundActionCreators }) => {
    const { createPage } = boundActionCreators
    return new Promise((resolve, reject) => {
      graphql(`
        {
          allMarkdownRemark {
            edges {
              node {
                fields {
                  slug
                }
              }
            }
          }
        }
      `
  ).then(result => {
    result.data.allMarkdownRemark.edges.map(({ node }) => {
        createPage({
          path: node.fields.slug,
          component: path.resolve(`./src/templates/page.tsx`),
          context: {
            // Data passed to context is available in page queries as GraphQL variables.
            slug: node.fields.slug,
          },
        })
      })
        resolve()
      })
    })
  }