Polyfill IntersectionObserver

[ximbong]

Summary

An error occurred when trying to polyfill IntersectionObserver as in the documentation.

Relevant information

An answer in this issue, with async function and await import fixed this. I'm not sure if this is anyhow environment related.

Environment (if relevant)

  System:
    OS: macOS 10.14.6
    CPU: (4) x64 Intel(R) Core(TM) i7-6567U CPU @ 3.30GHz
    Shell: 5.3 - /bin/zsh
  Binaries:
    Node: 10.15.3 - ~/.nvm/versions/node/v10.15.3/bin/node
    Yarn: 1.21.1 - ~/.yvm/shim/yarn
    npm: 6.4.1 - ~/.nvm/versions/node/v10.15.3/bin/npm
  Languages:
    Python: 2.7.16 - /usr/bin/python
  Browsers:
    Chrome: 79.0.3945.117
    Firefox: 69.0
    Safari: 13.0.4
  npmPackages:
    gatsby: ^2.13.3 => 2.18.18 
    gatsby-background-image: ^0.9.6 => 0.9.12 
    gatsby-image: ^2.2.33 => 2.2.37 
    gatsby-plugin-emotion: ^4.1.1 => 4.1.18 
    gatsby-plugin-layout: ^1.1.21 => 1.1.21 
    gatsby-plugin-manifest: ^2.2.1 => 2.2.34 
    gatsby-plugin-offline: ^2.2.1 => 2.2.10 
    gatsby-plugin-react-helmet: ^3.1.0 => 3.1.18 
    gatsby-plugin-robots-txt: ^1.5.0 => 1.5.0 
    gatsby-plugin-sitemap: ^2.2.25 => 2.2.25 
    gatsby-plugin-typescript: ^2.1.0 => 2.1.23 
    gatsby-source-contentful: ^2.1.6 => 2.1.73 

File contents (as in the documentation)

gastby-browser.js:

export const onClientEntry = () => {
  // IntersectionObserver polyfill for gatsby-background-image (Safari, IE)
  if (!(`IntersectionObserver` in window)) {
    import(`intersection-observer`)
    console.log(`# IntersectionObserver is polyfilled!`)
  }
}

[ximbong]

Closing this issue, as this I just found out it's ESlint related! no-unused-expressions

[alande-amorim]

indeed this did the trick for me