Make category pages work.

app/gatsby-node.js

@@ -1,7 +1,20 @@
-/**
- * Implement Gatsby's Node APIs in this file.
- *
- * See: https://www.gatsbyjs.org/docs/node-apis/
- */
+const fs = require("fs")
+const categories = JSON.parse(fs.readFileSync("src/data/categories.json"))
 
-// You can delete this file if you're not using it
+function createSlug (categoryName) {
+    const categoryNameLower = categoryName.toLowerCase();
+    return categoryNameLower.replace(" ", "-");
+};
+
+exports.createPages = ({ actions }) => {
+  const { createPage } = actions
+  categories.forEach(category => {
+    createPage({
+        path: createSlug(category.name),
+        component: require.resolve("./src/templates/categoryTemplate.js"),
+        context: {
+            categoryName: category.name
+        },
+      })
+    })
+}