gatsby-node.js

const path = require('path');
const { createFilePath } = require('gatsby-source-filesystem');

const createIndexPages = (createPage, posts) => {
  const indexPageTemplate = path.resolve('src/templates/index-page.js');
  const paginateSize = 6;

  // Split posts into arrays of length equal to number posts on each page/paginateSize
  const groupedPages = posts
    .filter(post => post.node.frontmatter.title.length > 0 && post.node.frontmatter.layout === 'post')
    .map((node, index, arr) =>
      (index % paginateSize === 0 ? arr.slice(index, index + paginateSize) : null))
    .filter(item => item);

  // Create new indexed route for each array
  return groupedPages.forEach((group, index, groups) => {
    const pageIndex = index === 0 ? '' : `p/${index + 1}`;
    const paginationRoute = `/${pageIndex}`;
    // Avoid showing `Previous` link on first page - passed to context
    const first = index === 0;
    // Avoid showing `Next` link if this is the last page - passed to context
    const last = index === groups.length - 1;

    return createPage({
      path: paginationRoute,
      component: indexPageTemplate,
      // layout: 'index',
      context: {
        group,
        first,
        last,
        index: index + 1,
      },
    });
  });
};

const createPostPages = (createPage, posts) => {
  const blogPostTemplate = path.resolve('./src/templates/blog-post.js');

  return posts.forEach(({ node }) => {
    createPage({
      path: node.frontmatter.path || node.fields.slug,
      component: blogPostTemplate,
      context: {
        // Data passed to context is available
        // in page queries as GraphQL variables.
        slug: node.fields.slug,
        readNext: node.frontmatter.readNext,
      },
    });
  });
};

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 = ({ graphql, actions }) => {
  const { createPage } = actions;
  return new Promise((resolve, reject) => {
    graphql(`
      {
        allMarkdownRemark(sort: { order: DESC, fields: [frontmatter___date] }, limit: 1000) {
          edges {
            node {
              id
              excerpt(pruneLength: 250)
              frontmatter {
                title
                date(formatString: "MMMM YYYY")
                description
                path
                layout
                author
                category
                readNext
                issueNumber
                # noindex
              }
              fields {
                slug
              }
            }
          }
        }
      }
    `).then((result) => {
      if (result.errors) {
        return reject(result.errors);
      }
      createPostPages(createPage, result.data.allMarkdownRemark.edges);
      createIndexPages(createPage, result.data.allMarkdownRemark.edges);
      return resolve();
    });
  });
};