gatsby-node.js

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

module.exports.onCreateNode = ({ node, actions }) => {
  const { createNodeField } = actions;
  if (node.internal.type === "MarkdownRemark") {
    const slug = path.basename(node.fileAbsolutePath, ".md");
    createNodeField({
      node,
      name: "slug",
      value: slug,
    });
  }
};

exports.createPages = async ({ graphql, actions }) => {
  const { createPage } = actions;
  const postTemplate = path.resolve("./src/templates/post/post.js");
  const tagTemplate = path.resolve("./src/templates/tag/tag.js");

  const res = await graphql(`
    query {
      postsRemark: allMarkdownRemark(
        sort: { order: DESC, fields: [frontmatter___date] }
        limit: 2000
      ) {
        edges {
          node {
            fields {
              slug
            }
            frontmatter {
              tags
            }
          }
        }
      }
      tagsGroup: allMarkdownRemark(limit: 2000) {
        group(field: frontmatter___tags) {
          fieldValue
        }
      }
    }
  `);
  const posts = res.data.postsRemark.edges;
  posts.forEach((edge) => {
    createPage({
      component: postTemplate,
      path: `/posts/${edge.node.fields.slug}`,
      context: {
        slug: edge.node.fields.slug,
      },
    });
  });

  const tags = res.data.tagsGroup.group;
  tags.forEach((tag) => {
    createPage({
      component: tagTemplate,
      path: `/tags/${_.kebabCase(tag.fieldValue)}/`,
      context: {
        tag: tag.fieldValue,
      },
    });
  });
};