gatsby-node.js

const path = require('path');

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

    const blogTemplate = path.resolve('src/templates/blog.js');
    const eventTemplate = path.resolve('src/templates/event.js');

    return graphql(
        `{
            allMarkdownRemark {
                edges {
                    node {
                        id
                        frontmatter {
                            slug
                        }

                    }
                }
            }
        }`
    ).then(res => {
        if (res.errors) {
            return Promise.reject(errors);
        }


        res.data.allMarkdownRemark.edges.map(element => {

            let slug = element.node.frontmatter.slug;

            if (slug) {
                //create page for blog using template
                if (slug.includes(`/blog/`)) {
                    createPage({
                        path: slug,
                        component: blogTemplate
                    })
                } else if (slug.includes(`/events/`)) {
                    createPage({
                        path: slug,
                        component: eventTemplate
                    })
                }
            }
            
        });
    })
}