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Using theme options in gatsby-config.js

Gatsby themes allow you to pass in options in the same way plugins get options.

module.exports = {
plugins: [
resolve: "gatsby-theme-awesome",
options: {
myThing: true,
blogPostFormat: "mdx"

Since gatsby-config has historically exported an object, as seen above, we needed to add a way to grab the options. This is why the function gatsby-config exists, which we can use in our theme to control which plugins are added (or anything else).

module.exports = options => {
const plugins = [];
if (options.blogPostFormat === "mdx") {
resolve: `gatsby-plugin-mdx`
return {

Note that trying to use the function gatsby-config in the root of a site will fail because there's nowhere to get the options from.