gatsby-node.js

/**
 * Implement Gatsby's Node APIs in this file.
 *
 * See: https://www.gatsbyjs.org/docs/node-apis/
 */

// You can delete this file if you're not using it
const path = require('path');
const _ = require('lodash');

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

  const blogPostTemplate = path.resolve('src/templates/blogPost.js');
  const tagTemplate = path.resolve('src/templates/tags.js');

  return graphql(`
    {
      allMarkdownRemark(sort: { frontmatter: { date: DESC } }, limit: 1000) {
        edges {
          node {
            frontmatter {
              path
              tags
            }
          }
        }
      }
    }
  `).then(result => {
    if (result.errors) {
      return Promise.reject(result.errors);
    }

    const posts = result.data.allMarkdownRemark.edges;

    // Make post pages
    posts.forEach(({ node }) => {
      createPage({
        path: node.frontmatter.path,
        component: blogPostTemplate,
        context: {} // additional data can be passed via context
      });
    });

    // 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
        }
      });
    });
  });
};