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/blog.js")
  const tagTemplate = path.resolve("src/templates/tags.js");

  const result = await graphql(`
    {
      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.fields.slug,
  //     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,
      },
    });
  });
};