gatsby-node.js

/**
 * Implement Gatsby's Node APIs in this file.
 *
 * See: https://www.gatsbyjs.com/docs/node-apis/
 */

// You can delete this file if you're not using it

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

exports.onCreateNode = ({ node, getNode, actions }) => {
  // this will show on start up
  // console.log(node.internal.type)

  const { createNodeField } = actions
  if (node.internal.type === `MarkdownRemark`) {
    // slug is the route, 3rd param is basepath which is optional
    const slug = createFilePath({ node, getNode })

    createNodeField({
      node,
      name: `slug`,
      value: slug,
    })
  }
}

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

  return graphql(`
    {
      allMarkdownRemark {
        edges {
          node {
            fields {
              slug
            }
          }
        }
      }
    }
  `).then(result => {
    result.data.allMarkdownRemark.edges.forEach(({ node }) => {
      createPage({
        path: node.fields.slug,
        component: path.resolve(`./src/templates/blog-post.js`),
        context: {
          slug: node.fields.slug,
        },
      })
    })
  })
}