Example with Gatsby Node APIs

gatsby-node.js

const path = require('path')
const { createPages } = require('gatsby/node')

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

  const result = await graphql(`
    {
      allMarkdownRemark {
        edges {
          node {
            fields {
              slug
            }
          }
        }
      }
    }
  `)
    .then(res => {
      if (res.errors) {
        throw res.errors
      }
      return res.data
    })

  const templates = {
    blogPost: path.resolve('src/templates/blog-post.js')
  }

  result.allMarkdownRemark.edges.forEach(({ node }) => {
    createPage({
      component: templates.blogPost,
      path: node.fields.slug,
      context: {
        slug
      }
    })
  })
})