homepage/src/templates/siteTemplate.js

import React, { useEffect } from "react"
import { graphql } from "gatsby"
import Layout from "../components/layout"
import { MDXRenderer } from "gatsby-plugin-mdx"

export default function Template({
  data, // this prop will be injected by the GraphQL query below.
}) {
  const { mdx } = data // data.markdownRemark holds your post data
  const { frontmatter, body } = mdx

  useEffect(() => {
    document.title = frontmatter.title
  }, [frontmatter.title])

  return (
    <Layout>
      <MDXRenderer>{body}</MDXRenderer>
    </Layout>
  )
}

export const pageQuery = graphql`
  query($path: String!) {
    mdx(frontmatter: { path: { eq: $path } }) {
      body
      frontmatter {
        title
      }
    }
  }
`