gatsby-node.js

const path = require("path");
const _ = require("lodash");




//Generate slug for blog posts path.
exports.onCreateNode = ({ node, actions }) => {
  const { createNodeField } = actions;
  let slug;
  if (node.internal.type === "MarkdownRemark") {
    slug = path.basename(node.fileAbsolutePath, ".md");
    createNodeField({
      node,
      name: "slug",
      value: slug,
    })
    console.log(slug);
  }
}



//Create pages and coresponding url for each markdown file.
exports.createPages = async ({ graphql, actions }) => {
  const { createPage } = actions
  const response = await graphql(`
      query {
        site {
          siteMetadata {
            domain: siteUrl
          }
        }
        allMarkdownRemark (sort:{ order: ASC, fields: [frontmatter___date]}
          limit: 1000
        ){
          edges {
            node {
              fields {
                slug
              }
              frontmatter {
                tags
                title
              }
            }
          }

        }

        tagsGroup: allMarkdownRemark(limit: 2000) {
            group(field: frontmatter___tags) {
              fieldValue
            }
        }
      }
    `)

  // Create blog-list pages
  const articles = response.data.allMarkdownRemark.edges;

  const postsPerPage = 10;

  const numPages = Math.ceil(articles.length / postsPerPage);


  Array.from({ length: numPages }).forEach((_, i) => {
    createPage({
      path: i === 0 ? `/blog/` : `/blog/${i + 1}/`,
      component: path.resolve("./src/templates/blog-list.js"),
      context: {
        limit: postsPerPage,
        skip: i * postsPerPage,
        numPages,
        currentPage: i + 1,
      },
    })
  })

  //create page for each post

  articles.forEach(({ node }, index) => {
    createPage({
      path: `/blog/${node.fields.slug}/`,
      component: path.resolve("./src/templates/blog-post.js"),
      context: {
        slug: node.fields.slug,
        prev: index === 0 ? null : articles[index - 1].node,
        next: index === articles.length - 1 ? null : articles[index + 1].node
      },
    })
  })

  // Extract tag data from query and create page
  response.data.tagsGroup.group.forEach(tag => {
    createPage({
      path: `/tags/${_.kebabCase(tag.fieldValue)}/`,
      component: path.resolve("./src/templates/tags.js"),
      context: {
        tag: tag.fieldValue,
      },
    })
  })
}