gatsby-node.js

const path = require('path');

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

  const blogPostTemplate = path.resolve(`src/templates/blog-post.js`);

  return graphql(`{
    allMarkdownRemark(
      sort: { order: DESC, fields: [frontmatter___date] }
      limit: 1000
    ) {
      edges {
        node {
          excerpt(pruneLength: 250)
          html
          id
          frontmatter {
            path
            date
            title
          }
        }
      }
    }
  }`).then(result => {
      if (result.errors) {
        return Promise.reject(result.errors);
      }
      result.data.allMarkdownRemark.edges.forEach(({ node }) => {
      createPage({
        path: node.frontmatter.path,
        component: blogPostTemplate,
        context: {} // additional data can be passed via context
      });
    });
  });
}