Gatsby Browser APIs
The file gatsby-browser.js lets you respond to Gatsby-specific events within the browser, and wrap your page components in additional global components. The Gatsby Browser API gives you many options for interacting with the client-side of Gatsby. To use Browser APIs, create a file in the root of your site at gatsby-browser.js.
https://www.gatsbyjs.com/docs/reference/config-files/gatsby-browser/#wrapPageElement
