gatsby-node.js

const resolvableExtensions = () => [`.ts`, `.tsx`]

function onCreateBabelConfig({ actions }, pluginOptions) {
  actions.setBabelPreset({
    name: `@babel/preset-typescript`,
  })
}

function onCreateWebpackConfig({ actions, loaders }) {
  const jsLoader = loaders.js()

  if (!jsLoader) {
    return
  }

  actions.setWebpackConfig({
    module: {
      rules: [
        {
          test: /\.tsx?$/,
          use: jsLoader,
        },
      ],
    },
  })
}

exports.resolvableExtensions = resolvableExtensions
exports.onCreateBabelConfig = onCreateBabelConfig
exports.onCreateWebpackConfig = onCreateWebpackConfig