Triển khai code mới (ok)

C:\xampp\htdocs\html\src\main.js

import Vue from 'vue'
import App from './App'
import router from './router'
Vue.config.productionTip = false;
new Vue({
  el: '#app',
  router,
  components: { App },
  template: '<App/>'
})

C:\xampp\htdocs\html\src\router\index.js

import Vue from 'vue';
import Router from 'vue-router';
Vue.use(Router);
const routes =  [
  {
    path: "/",
    alias: "/tutorials",
    name: "tutorials",
    component: () => import("../components/TutorialsList")
  },
  {
    path: "/tutorials/:id",
    name: "tutorial-details",
    component: () => import("../components/Tutorial")
  },
  {
    path: "/add",
    name: "add",
    component: () => import("../components/AddTutorial")
  }
];
export default new Router({
  routes: routes
})

C:\xampp\htdocs\html\db.json

{
  "tutorials": [
    { "id": 1, "title": "Title 1"},
    { "id": 2, "title": "Title 2"},
    { "id": 3, "title": "Title 3"},
    { "id": 4, "title": "Title 4"},
    { "id": 5, "title": "Title 5"}
  ]
}

C:\xampp\htdocs\html\src\App.vue

<template>
  <div id="app">
    <nav class="navbar navbar-expand navbar-dark bg-dark">
      <router-link to="/" class="navbar-brand">bezKoder</router-link>
      <div class="navbar-nav mr-auto">
        <li class="nav-item">
          <router-link to="/tutorials" class="nav-link">Tutorials</router-link>
        </li>
        <li class="nav-item">
          <router-link to="/add" class="nav-link">Add</router-link>
        </li>
      </div>
    </nav>
    <div class="container mt-3">
      <router-view />
    </div>
  </div>
</template>
<script>
export default {
  name: "app"
};
</script>

C:\xampp\htdocs\html\src\http-common.js

import axios from "axios";
export default axios.create({
  baseURL: "http://localhost:3000",
  headers: {
    "Content-type": "application/json"
  }
});

C:\xampp\htdocs\html\src\components\AddTutorial.vue

<template>
  <div class="submit-form">
    <div v-if="!submitted">
      <div class="form-group">
        <label for="title">Title</label>
        <input
          type="text"
          class="form-control"
          id="title"
          required
          v-model="tutorial.title"
          name="title"
        />
      </div>

      <div class="form-group">
        <label for="description">Description</label>
        <input
          class="form-control"
          id="description"
          required
          v-model="tutorial.description"
          name="description"
        />
      </div>

      <button @click="saveTutorial" class="btn btn-success">Submit</button>
    </div>

    <div v-else>
      <h4>You submitted successfully!</h4>
      <button class="btn btn-success" @click="newTutorial">Add</button>
    </div>
  </div>
</template>

<script>
import TutorialDataService from "../services/TutorialDataService";

export default {
  name: "add-tutorial",
  data() {
    return {
      tutorial: {
        id: null,
        title: "",
        description: "",
        published: false
      },
      submitted: false
    };
  },
  methods: {
    saveTutorial() {
      var data = {
        title: this.tutorial.title,
        description: this.tutorial.description
      };

      TutorialDataService.create(data)
        .then(response => {
          this.tutorial.id = response.data.id;
          console.log(response.data);
          this.submitted = true;
        })
        .catch(e => {
          console.log(e);
        });
    },
    
    newTutorial() {
      this.submitted = false;
      this.tutorial = {};
    }
  }
};
</script>

<style>
.submit-form {
  max-width: 300px;
  margin: auto;
}
</style>

C:\xampp\htdocs\html\src\components\Tutorial.vue

<template>
  <div v-if="currentTutorial" class="edit-form">
    <h4>Tutorial</h4>
    <form>
      <div class="form-group">
        <label for="title">Title</label>
        <input type="text" class="form-control" id="title"
          v-model="currentTutorial.title"
        />
      </div>
      <div class="form-group">
        <label for="description">Description</label>
        <input type="text" class="form-control" id="description"
          v-model="currentTutorial.description"
        />
      </div>

      <div class="form-group">
        <label><strong>Status:</strong></label>
        {{ currentTutorial.published ? "Published" : "Pending" }}
      </div>
    </form>

    <button class="badge badge-primary mr-2"
      v-if="currentTutorial.published"
      @click="updatePublished(false)"
    >
      UnPublish
    </button>
    <button v-else class="badge badge-primary mr-2"
      @click="updatePublished(true)"
    >
      Publish
    </button>

    <button class="badge badge-danger mr-2"
      @click="deleteTutorial"
    >
      Delete
    </button>

    <button type="submit" class="badge badge-success"
      @click="updateTutorial"
    >
      Update
    </button>
    <p>{{ message }}</p>
  </div>

  <div v-else>
    <br />
    <p>Please click on a Tutorial...</p>
  </div>
</template>

<script>
import TutorialDataService from "../services/TutorialDataService";

export default {
  name: "tutorial",
  data() {
    return {
      currentTutorial: null,
      message: ''
    };
  },
  methods: {
    getTutorial(id) {
      TutorialDataService.get(id)
        .then(response => {
          this.currentTutorial = response.data;
          console.log(response.data);
        })
        .catch(e => {
          console.log(e);
        });
    },

    updatePublished(status) {
      var data = {
        id: this.currentTutorial.id,
        title: this.currentTutorial.title,
        description: this.currentTutorial.description,
        published: status
      };

      TutorialDataService.update(this.currentTutorial.id, data)
        .then(response => {
          console.log(response.data);
          this.currentTutorial.published = status;
          this.message = 'The status was updated successfully!';
        })
        .catch(e => {
          console.log(e);
        });
    },

    updateTutorial() {
      TutorialDataService.update(this.currentTutorial.id, this.currentTutorial)
        .then(response => {
          console.log(response.data);
          this.message = 'The tutorial was updated successfully!';
        })
        .catch(e => {
          console.log(e);
        });
    },

    deleteTutorial() {
      TutorialDataService.delete(this.currentTutorial.id)
        .then(response => {
          console.log(response.data);
          this.$router.push({ name: "tutorials" });
        })
        .catch(e => {
          console.log(e);
        });
    }
  },
  mounted() {
    this.message = '';
    this.getTutorial(this.$route.params.id);
  }
};
</script>

<style>
.edit-form {
  max-width: 300px;
  margin: auto;
}
</style>

C:\xampp\htdocs\html\src\components\TutorialsList.vue

<template>
  <div class="list row">
    <div class="col-md-8">
      <div class="input-group mb-3">
        <input type="text" class="form-control" placeholder="Search by title"
          v-model="title"/>
        <div class="input-group-append">
          <button class="btn btn-outline-secondary" type="button"
            @click="searchTitle"
          >
            Search
          </button>
        </div>
      </div>
    </div>
    <div class="col-md-6">
      <h4>Tutorials List</h4>
      <ul class="list-group">
        <li class="list-group-item" :class="{ active: index == currentIndex }" v-for="(tutorial, index) in tutorials" :key="index" @click="setActiveTutorial(tutorial, index)">
          {{ tutorial.title }}
        </li>
      </ul>

      <button class="m-3 btn btn-sm btn-danger" @click="removeAllTutorials">
        Remove All
      </button>
    </div>
    <div class="col-md-6">
      <div v-if="currentTutorial">
        <h4>Tutorial</h4>
        <div>
          <label><strong>Title:</strong></label> {{ currentTutorial.title }}
        </div>
        <div>
          <label><strong>Description:</strong></label> {{ currentTutorial.description }}
        </div>
        <div>
          <label><strong>Status:</strong></label> {{ currentTutorial.published ? "Published" : "Pending" }}
        </div>

        <router-link :to="'/tutorials/' + currentTutorial.id" class="badge badge-warning">Edit</router-link>
      </div>
      <div v-else>
        <br />
        <p>Please click on a Tutorial...</p>
      </div>
    </div>
  </div>
</template>

<script>
import TutorialDataService from "../services/TutorialDataService";

export default {
  name: "tutorials-list",
  data() {
    return {
      tutorials: [],
      currentTutorial: null,
      currentIndex: -1,
      title: ""
    };
  },
  methods: {
    retrieveTutorials() {
      TutorialDataService.getAll()
        .then(response => {
          this.tutorials = response.data;
          console.log(response.data);
        })
        .catch(e => {
          console.log(e);
        });
    },

    refreshList() {
      this.retrieveTutorials();
      this.currentTutorial = null;
      this.currentIndex = -1;
    },

    setActiveTutorial(tutorial, index) {
      this.currentTutorial = tutorial;
      this.currentIndex = tutorial ? index : -1;
    },

    removeAllTutorials() {
      TutorialDataService.deleteAll()
        .then(response => {
          console.log(response.data);
          this.refreshList();
        })
        .catch(e => {
          console.log(e);
        });
    },
    
    searchTitle() {
      TutorialDataService.findByTitle(this.title)
        .then(response => {
          this.tutorials = response.data;
          this.setActiveTutorial(null);
          console.log(response.data);
        })
        .catch(e => {
          console.log(e);
        });
    }
  },
  mounted() {
    this.retrieveTutorials();
  }
};
</script>

<style>
.list {
  text-align: left;
  max-width: 750px;
  margin: auto;
}
</style>

C:\xampp\htdocs\html\src\services\TutorialDataService.js

import http from "../http-common";
class TutorialDataService {
  getAll() {
    return http.get("/tutorials");
  }
  get(id) {
    return http.get(`/tutorials/${id}`);
  }
  create(data) {
    return http.post("/tutorials", data);
  }
  update(id, data) {
    return http.put(`/tutorials/${id}`, data);
  }
  delete(id) {
    return http.delete(`/tutorials/${id}`);
  }
  deleteAll() {
    return http.delete(`/tutorials`);
  }
  findByTitle(title) {
    return http.get(`/tutorials?title=${title}`);
  }
}
export default new TutorialDataService();