createPage.js

exports.createPages = ({ actions, graphql }) => {
  const { createPage } = actions;
  // A template for generating a new page from
  const notesTemplate = path.resolve(`src/templates/notes.js`);

  // A promise which collects all the MarkdownRemark nodes and then generates pages
  return new Promise((resolve, reject) => {
    // Our graphql query wrapped in a resolve 
    // Note how you can add more information in the allMarkdownRemark parameters to fine tune the query
    resolve(graphql(`
    {
      allMarkdownRemark(
        sort: { order: DESC, fields: [frontmatter___date] }
        limit: 1000
      ) {
        edges {
          node {
            fields{
              slug
            }
            frontmatter {
              title
            }
          }
        }
      }
    }`).then(result => {
        // If there are errors then report them and reject.
        if (result.errors) {
          console.error(results.errors);
          return reject(result.errors);
        }

        // Otherwise generate the pages for each node we found
        result.data.allMarkdownRemark.edges.forEach(({ node }) => {
          createPage({
            path: node.fields.slug,
            component: notesTemplate,
            context: {
              slug: node.fields.slug,
            }
          })
        })
        return
      })
    )
  });
}