added type declarations

src/pages/projects/index.tsx

@@ -2,7 +2,7 @@ import React from "react";
 import Navbar from '../../components/navbar';
 import Item from "../../components/item";
 
-export default () => (
+export default (): JSX.Element => (
   <>
     <Navbar />
     <Item
@@ -19,4 +19,4 @@ export default () => (
       subtitle="subtitle"
     />
   </>
-);
+);

src/templates/note.tsx

@@ -3,13 +3,8 @@ import Navbar from '../components/navbar';
 import { graphql } from "gatsby";
 import { MDXRenderer } from 'gatsby-plugin-mdx';
 
-export default ({
-  data
-}) => {
-  let {
-    frontmatter,
-    body
-  } = data.mdx;
+export default ({ data }) => {
+  const { frontmatter, body } = data.mdx;
 
   return <>
     <Navbar />
@@ -29,4 +24,4 @@ query NotesIndexQuery($id: String!) {
     tableOfContents
     body
   }
-}`;
+}`;

src/templates/notes.tsx

@@ -8,7 +8,7 @@ import Navbar from "../components/navbar";
 import { graphql } from "gatsby";
 import style from "./notes.module.css";
 
-export default ({ data, pageContext }) => {
+export default ({ data, pageContext }): JSX.Element => {
   const posts = data.allMdx.edges;
   const { currentPage, numPages, rootPath } = pageContext;
   let prevPageLink = null;