Use promise in gatsby-node.

app/gatsby-node.js

@@ -1,21 +1,18 @@
-const fs = require("fs")
-const categories = JSON.parse(fs.readFileSync("src/data/categories.json"))
-var slugify = require('slugify')
+const fs = require('fs');
+
+const categories = JSON.parse(fs.readFileSync('src/data/categories.json'));
+const slugify = require('slugify');
 
 exports.createPages = async function ({ actions, graphql }) {
-  const { createPage } = actions
-  categories.forEach(async function(category) {
-    const data = await graphql(`query categoryBooksQuery($categoryName: String) {
+  const { createPage } = actions;
+  await Promise.all(
+    categories.map(async (category) => {
+      const data = await graphql(
+        `
+          query categoryBooksQuery($categoryName: String) {
             allBooksJson(
-            filter: {
-                category: {
-                    eq: $categoryName
-                }
-            }
-            sort: {
-              fields: [rating]
-              order: DESC
-            }
+              filter: { category: { eq: $categoryName } }
+              sort: { fields: [rating], order: DESC }
             ) {
               edges {
                 node {
@@ -34,17 +31,19 @@ exports.createPages = async function ({ actions, graphql }) {
             }
           }
         `,
-    {categoryName: category.name})
-    console.log(category.name, data.data)
+        { categoryName: category.name },
+      );
+      console.log(category.name, data.data);
       createPage({
         path: slugify(category.name),
-        component: require.resolve("./src/templates/categoryTemplate.js"),
+        component: require.resolve('./src/templates/categoryTemplate.js'),
         context: {
           categoryName: category.name,
           data: data.data,
           image: category.emoji,
           limit: null,
         },
-      })
-    })
-}
+      });
+    }),
+  );
+};