Use promise in gatsby-node.

app/gatsby-node.js

@@ -1,50 +1,49 @@
-const fs = require("fs")
+const fs = require('fs');
-const categories = JSON.parse(fs.readFileSync("src/data/categories.json"))
+
-var slugify = require('slugify')
+const categories = JSON.parse(fs.readFileSync('src/data/categories.json'));
+const slugify = require('slugify');
 
 exports.createPages = async function ({ actions, graphql }) {
-  const { createPage } = actions
+  const { createPage } = actions;
-  categories.forEach(async function(category) {
+  await Promise.all(
-    const data = await graphql(`query categoryBooksQuery($categoryName: String) {
+    categories.map(async (category) => {
-        allBooksJson(
+      const data = await graphql(
-            filter: {
+        `
-                category: {
+          query categoryBooksQuery($categoryName: String) {
-                    eq: $categoryName
+            allBooksJson(
+              filter: { category: { eq: $categoryName } }
+              sort: { fields: [rating], order: DESC }
+            ) {
+              edges {
+                node {
+                  id
+                  title
+                  url
+                  rating
+                  author
+                  year
+                  category
+                  image_url
+                  description
+                  amazon_url
                 }
-            }
+              }
-            sort: {
-              fields: [rating]
-              order: DESC
-            }
-        ){
-          edges {
-            node {
-              id
-              title
-              url
-              rating
-              author
-              year
-              category
-              image_url
-              description
-              amazon_url
             }
           }
-        }
+        `,
-      }
+        { categoryName: category.name },
-    `,
+      );
-    {categoryName: category.name})
+      console.log(category.name, data.data);
-    console.log(category.name, data.data)
+      createPage({
-    createPage({
         path: slugify(category.name),
-        component: require.resolve("./src/templates/categoryTemplate.js"),
+        component: require.resolve('./src/templates/categoryTemplate.js'),
         context: {
-            categoryName: category.name,
+          categoryName: category.name,
-            data: data.data,
+          data: data.data,
-            image: category.emoji,
+          image: category.emoji,
-            limit: null,
+          limit: null,
         },
-      })
+      });
-    })
+    }),
-}
+  );
+};