gatsby-node.js

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

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

  const blogPostTemplate = path.resolve("src/templates/blogTemplate.js")
  const tagTemplate = path.resolve("src/templates/tagsTemplate.js")

  const result = await graphql(`
    {
      postsRemark: allMarkdownRemark(
        sort: { order: DESC, fields: [frontmatter___date] }
        limit: 2000
      ) {
        edges {
          node {
            frontmatter {
              path
            }
          }
        }
      }
      tagsGroup: allMarkdownRemark(limit: 2000) {
        group(field: frontmatter___tags) {
          fieldValue
        }
      }
    }
  `)

  // handle errors
  if (result.errors) {
    reporter.panicOnBuild(`Error while running GraphQL query.`)
    return
  }

  const posts = result.data.postsRemark.edges

  // Create post detail pages
  posts.forEach(({ node }) => {
    createPage({
      path: node.frontmatter.path,
      component: blogPostTemplate,
    })
  })

  
  // Extract tag data from query
  const tags = result.data.tagsGroup.group

  // Make tag pages
  tags.forEach(tag => {
    createPage({
      path: `/tags/${_.kebabCase(tag.fieldValue)}/`,
      component: tagTemplate,
      context: {
        tag: tag.fieldValue,
      },
    })
  })
}