feat: store state for posts by category

After clicking on each category, users can view posts of the category

Using GET_POSTS_BY_CATEGORY action and redeucer

frontend/src/post/Post.js

@@ -0,0 +1,12 @@
+import React, { Component } from 'react';
+import PropTypes from 'prop-types';
+import { Route, Link } from 'react-router-dom';
+
+const Post = props => (
+  <div>{props.post.author} - {props.post.title} - {props.post.body} - {props.post.voteScore}</div>
+)
+Post.PropTypes = {
+  post: PropTypes.object.isRequired
+}
+
+export default Post

frontend/src/post/action.js

@@ -0,0 +1,17 @@
+export const GET_POSTS_BY_CATEGORY = 'GET_POSTS_BY_CATEGORY'
+
+const getPostsByCategory = posts => ({
+        type: GET_POSTS_BY_CATEGORY,
+      	posts
+  }
+)
+
+export function fetchPostsByCategory(category) {
+  return function (dispatch) {
+    const url = `${process.env.REACT_APP_BACKEND}/${category}/posts`
+    return fetch( url, { headers: { 'Authorization': 'whatever-you-want' }, credentials: 'include' })
+    	.then((res) => res.json())
+      .then(data => dispatch(getPostsByCategory(data))
+    );
+  };
+}

frontend/src/post/reducer.js

@@ -0,0 +1,26 @@
+import { combineReducers } from 'redux'
+
+import {
+  GET_POSTS_BY_CATEGORY,
+} from './action'
+
+function getPostsByCategoriesReducer (state={
+    isFetching: true,
+    posts: []
+  }, action) {
+  const { posts } = action
+  console.log(posts)
+  switch (action.type) {
+    case GET_POSTS_BY_CATEGORY:
+      return Object.assign({}, state, {
+        isFetching: false,
+        posts
+      })
+    default:
+      return state
+  }
+}
+
+export default combineReducers({
+  getPostsByCategoriesReducer
+})