Creating the pages programmatically

1-gatsby-node.js

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

exports.onCreateNode = ({ node, actions, getNode }) => {
  const { createNodeField } = actions

  if (node.internal.type === `MarkdownRemark`) {
    const value = createFilePath({ node, getNode })
    const [month, day, year] = new Date(node.frontmatter.date)
      .toLocaleDateString("en-EN", {
        year: "numeric",
        month: "2-digit",
        day: "2-digit",
      })
      .split("/")
    const slug = value.replace("/blog/", "").replace(/\/$/, "")
    const url = `/blog/${year}/${month}/${day}${slug}`

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