gatsby-node.js

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

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

  const blogPost = path.resolve(`./src/templates/blog-post.js`);
  const result = await graphql(
    `
      {
        wpgraphql {
          posts {
            edges {
              node {
                slug
                title
              }
            }
          }
        }
      }
    `
  );

  if (result.errors) {
    throw result.errors;
  }

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

  posts.forEach((post, index) => {
    const previous = index === posts.length - 1 ? null : posts[index + 1].node;
    const next = index === 0 ? null : posts[index - 1].node;

    createPage({
      path: post.node.slug,
      component: blogPost,
      context: {
        slug: post.node.slug,
        previous,
        next,
      },
    });
  });
};

// Client only routes for preview
exports.onCreatePage = async ({ page, actions }) => {
  const { createPage } = actions;

  // page.matchPath is a special key that's used for matching pages
  // only on the client.
  if (page.path.match(/^\/preview/)) {
    page.matchPath = '/preview/*';

    // Update the page.
    createPage(page);
  }
};