Gatsby smooth anchor scroll + history “bug” fix

AnchorLink.jsx

import React from 'react'
import { string, node, func, shape } from 'prop-types'

import { scrollToHref } from './helpers'

const handleClick = ({ href, callback, history, event }) => {
  /* prevent normal link behavior */
  event.preventDefault()

  /* call the function */
  scrollToHref(href)

  /*
   * only push to browser history if it’s a new anchor
   *
   * this fixes the “bug” in Gatsby (react-router ?)
   * where the same hash can be pushed to history
   *
   * if you want to stick to default Gatsby behavior, remove the if condition block
   * and uncomment history.push(href) following it
   */
  if (history.location.hash !== href) {
    history.push(href)
  }

  /* Uncomment below line if you want default Gatsby behavior */
  // history.push(href)

  /* perform callback (example: closing modal sidebar) */
  if (callback) {
    callback()
  }
}

const AnchorLink = ({ href, history, callback, children, ...restProps }) => (
  <a
    href={href}
    onClick={event =>
      handleClick({
        href,
        callback, // optional callback, I use it to close modal sidebar
        history, // history object props that layout and pages have
        event,
      })
    }
    {...restProps}
  >
    {children}
  </a>
)

AnchorLink.propTypes = {
  href: string.isRequired,
  callback: func,
  children: node.isRequired,
  history: shape({
    push: func.isRequired,
    location: shape({
      hash: string.isRequired,
    }).isRequired,
  }).isRequired,
}

AnchorLink.defaultProps = {
  callback: undefined,
}

export default AnchorLink

HashChangeHandler.jsx

import { PureComponent } from 'react'
// npm install smoothscroll-polyfill
// this is a polyfill for Safari
import smoothscroll from 'smoothscroll-polyfill'

import { performScroll, scrollToHref } from './helpers'

const handleHashChange = () => {
  if (window.location.hash) {
    scrollToHref(window.location.hash)
  } else {
    /* hash doesn’t exist, meaning it just got removed. scroll to the very top */
    performScroll(0)
  }
}

export default class HashChangeHandler extends PureComponent {
  componentDidMount = () => {
    smoothscroll.polyfill()
    window.onhashchange = handleHashChange
  }

  render() {
    return null
  }
}

helpers.js

export const performScroll = (top) => {
  /* invoke scroll, with behavior smooth (not supported in Safari as of writing) */
  window.scrollTo({
    behavior: 'smooth',
    top,
  })
}

export const scrollToHref = (href) => {
  /* destination element to scroll to */
  const destinationElement = document.querySelector(href)

  performScroll(destinationElement.offsetTop)
}

layout.jsx

import React from 'react'
import HashChangeHandler from './HashChangeHandler'

const Layout = ({ children }) => (
  <div>
    <header>Header</header>
    <nav>Nav</nav>
    {children}
    <footer></footer>
    <HashChangeHandler />
  </div>
)

// if you’re using Gatsby v1, change children to be a function, as such: children()

export default Layout

This worked very well for me, thank you.

Now I have adjusted my site to fetch all its content from Markdown-files with GraphQL, and it's not working anymore. I put the anchor link destination in "h2" tags, like h2 id="1">Section Title< /h2>. Do you know why this could happen, and any workaround for this problem?