gatsby-node.js

const path = require('path')

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

    return new Promise((resolve, reject)=> {
        const courseOverviewTemplate = path.resolve('src/templates/courseOverview.js')
        resolve(
            graphql(`
            query {
            allMarkdownRemark {
                edges {
                    node {
                        frontmatter {
                            path
                        }
                    }
                }
            }
        }
            `).then(result => {
                result.data.allMarkdownRemark.edges.forEach(({node})=> {
                    const path = node.frontmatter.path
                    createPage({
                        path, 
                        component: courseOverviewTemplate,
                        context: {
                            pathSlug: path
                        }
                    })
                    resolve()
                })
            })
        )
    })
})