gatsby-node.js

const path = require('path');
const _ = require('lodash');
const webpackLodashPlugin = require('lodash-webpack-plugin');

exports.onCreateNode = ({ node, boundActionCreators, getNode }) => {
  const { createNodeField } = boundActionCreators;
  let slug;
  if (node.internal.type === 'MarkdownRemark') {
    const fileNode = getNode(node.parent);
    const parsedFilePath = path.parse(fileNode.relativePath);
    if (
      Object.prototype.hasOwnProperty.call(node, 'frontmatter') &&
      Object.prototype.hasOwnProperty.call(node.frontmatter, 'slug')
    ) {
      slug = `/${_.kebabCase(node.frontmatter.slug)}`;
    }
    if (
      Object.prototype.hasOwnProperty.call(node, 'frontmatter') &&
      Object.prototype.hasOwnProperty.call(node.frontmatter, 'title')
    ) {
      slug = `/${_.kebabCase(node.frontmatter.title)}`;
    } else if (parsedFilePath.name !== 'index' && parsedFilePath.dir !== '') {
      slug = `/${parsedFilePath.dir}/${parsedFilePath.name}/`;
    } else if (parsedFilePath.dir === '') {
      slug = `/${parsedFilePath.name}/`;
    } else {
      slug = `/${parsedFilePath.dir}/`;
    }
    createNodeField({ node, name: 'slug', value: slug });
  }
};

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

  return new Promise((resolve, reject) => {
    const blogPage = path.resolve('src/templates/blog.jsx');
    const lessonPage = path.resolve('src/templates/lesson.jsx');
    const tagPage = path.resolve('src/templates/tag.jsx');
    resolve(
      graphql(
        `{
          allMarkdownRemark(filter: {frontmatter: {type: {ne: "post"}}}) {
            edges {
              node {
                frontmatter {
                  tags
                  programming_language
                  type
                  language
                }
                fields {
                  slug
                }
              }
            }
          }
        }`
      ).then(result => {
        if (result.errors) {
          /* eslint no-console: "off" */
          console.log(result.errors);
          reject(result.errors);
        }

        const tagSet = new Set();
        result.data.allMarkdownRemark.edges.forEach(edge => {
          if (edge.node.frontmatter.tags) {
            edge.node.frontmatter.tags.forEach(tag => {
              tagSet.add(tag);
            });
          }

          if (edge.node.frontmatter.type === 'lesson') {
            createPage({
              path: `/${edge.node.frontmatter.language.toLowerCase()}/${edge.node.frontmatter.type}/${edge.node.frontmatter.programming_language}${edge.node.fields.slug}`,
              component: lessonPage,
              context: {
                slug: edge.node.fields.slug,
                programming_language: edge.node.frontmatter.programming_language,
                language: edge.node.frontmatter.language
              }
            });
          }
        });

        const tagList = Array.from(tagSet);
        tagList.forEach(tag => {
          createPage({
            path: `/tags/${_.kebabCase(tag)}/`,
            component: tagPage,
            context: {
              tag
            }
          });
        });
      })
      // .then(() => {
      //   createPage({
      //     path: `/blog`,
      //     component: blogPage,
      //     context: {}
      //   });
      // })
    );
  });
};

exports.modifyWebpackConfig = ({ config, stage }) => {
  if (stage === 'build-javascript') {
    config.plugin('Lodash', webpackLodashPlugin, null);
  }
};