gatsby-node.js

const path = require(`path`);
const { createFilePath } = require(`gatsby-source-filesystem`);
const titleCase = require('title-case').titleCase;

const uniq = require('lodash').uniq;
const includes = require('lodash').includes;

async function asyncForEach(array, callback) {
  for (let index = 0; index < array.length; index++) {
    await callback(array[index], index, array);
  }
}

exports.onCreateNode = ({ node, getNode, actions }) => {
  const { createNodeField } = actions;
  if (node.internal.type === `MarkdownRemark`) {
    const slug = createFilePath({ node, getNode, basePath: `pages` });
    createNodeField({
      node,
      name: `slug`,
      value: slug,
    });
  }
};

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

  const result = await graphql(`
    query {
      allMarkdownRemark {
        edges {
          node {
            frontmatter {
              title
              intro
              image {
                twitterCard: childImageSharp {
                  fixed(quality: 100) {
                    src
                  }
                }
                banner: childImageSharp {
                  fixed(quality: 100, width: 1600) {
                    src
                  }
                }
              }
            }
            fields {
              slug
            }
            html
          }
        }
      }
    }
  `);

  const allLinksQuery = await graphql(`
    query {
      allDataYaml {
        edges {
          node {
            links {
              categories
              charity_url
              countries
              description
              featured
              tags
              title
              type
              url
            }
          }
        }
      }
    }
  `);

  const allLinks = allLinksQuery.data.allDataYaml.edges[0].node.links;

  await asyncForEach(result.data.allMarkdownRemark.edges, async ({ node }) => {
    const {
      frontmatter,
      fields: { slug },
      html,
    } = node;

    const sanitizedSlug = slug.replace(/^\/|\/$/g, '');
    const linksForThisCategory = allLinks.filter(link =>
      includes(link.categories, sanitizedSlug)
    );

    createPage({
      path: slug,
      component: path.resolve(`./src/templates/category.jsx`),
      context: {
        category: frontmatter,
        html,
        links: linksForThisCategory,
        slug,
      },
    });
  });

  let allTags = [];

  allLinks.forEach(link => {
    allTags = [...allTags, ...link.categories];
  });

  allTags = uniq(allTags);

  await asyncForEach(allTags, async tag => {
    const sanitizedTag = tag.replace(/^\/|\/$/g, '');
    const linksForTag = allLinks.filter(link =>
      includes(link.tags, sanitizedTag)
    );

    // The tag name with the dashes replaced with spaces and the first letter in each word capitalised.
    const humanReadableTag = titleCase(tag);

    createPage({
      path: `/tags/${tag}`,
      component: path.resolve(`./src/templates/tag.jsx`),
      context: { tag: humanReadableTag, links: linksForTag },
    });
  });
};