gatsby-node.js

const _ = require('lodash')
const Promise = require('bluebird')
const path = require('path')
const { createFilePath } = require('gatsby-source-filesystem')

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

  return new Promise((resolve, reject) => {
    const blogPostTemplate = path.resolve('./src/templates/blog-post.js')
    const tagTemplate = path.resolve("./src/templates/tags.js")
    resolve(
      graphql(
        `
          {
            allMarkdownRemark(limit: 1000) {
              edges {
                node {
                  frontmatter {
                    path
                    tags
                  }
                }
              }
            }
          }
        `
      ).then(result => {
        if (result.errors) {
          console.log(result.errors)
          reject(result.errors)
        }

        // Create blog posts pages.
        const posts = result.data.allMarkdownRemark.edges;

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

        /*// Tag pages:
        let tags = [];
        // Iterate through each post, putting all found tags into `tags`
        _.each(posts, edge => {
          if (_.get(edge, "node.frontmatter.tags")) {
            tags = tags.concat(edge.node.frontmatter.tags);
          }
        });
        // Eliminate duplicate tags
        tags = _.uniq(tags);

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

      })
    )
  })
}