获取请求在Angular 5 app中抛出404错误

Question

我是Angular的新手。我正在创建一个演示视频播放器应用程序，关注youtube系列，但我很惊讶我无法获取数据以获取我的获取请求。我正在使用Angular 5.2.10.Below是我的文件和代码：

server.js：



    const express = require('express');
    const bodyParser = require('body-parser');
    const path = require('path');
    const api = require('./server/routes/api');
    const port = 3000;
    const app = express();

    app.use(express.static(path.join(__dirname,'dist')));
    app.use(bodyParser.urlencoded({extended:true}));
    app.use(bodyParser.json());
    app.use('/api',api);

    app.get('*',(req,res)=>{
        res.sendFile(path.join(__dirname,'dist/index.html'));
    });

    app.listen(port,function(){
        console.log("server running on localhost"+port);
    });

api.js：



        const express = require('express');
        const router = express.Router();
        const mongoose = require('mongoose');
        const Video = require('../models/video');
        const
    db="mongodb://usersubhash:subhashpwd@ds217350.mlab.com:17350/videoplayer";
        mongoose.Promise = global.Promise;
        mongoose.connect(db,function(err){
            if(err){
                console.log("Error!"+err);
            }
        });
        router.get('/videos',function(req,res){
            //res.send('api works');
            Video.find({}).exec(function(err,videos){
                if(err){
                    console.log("error retrieving videos");
                }else{
                    res.json(videos);
                }
            });
        });
        module.exports = router;

的Video.js：



    const mongoose = require('mongoose');
    const Schema = mongoose.Schema;
    const videoSchema = new Schema({
        title:String,
        url:String,
        description:String
    });

    module.exports = mongoose.model('video',videoSchema,'videos');

video.ts：



    export class Video {
        _id:string;
        title:string;
        url:string;
        description:string
    }

environment.ts


export const environment = {
  production: false,
  apiUrl: 'http://localhost:3000'
};

video.service.ts :(其中我有getVideos（）方法）



    import { Injectable } from '@angular/core';
    import {Http,Response} from '@angular/http';
    import 'rxjs/add/operator/map';
    @Injectable()
    export class VideoService {

      constructor(private _http:Http) { }
      private _getUrl = `${environment.apiUrl}/api/videos`;
      getVideos(){
        return this._http.get(this._getUrl).map((response:Response)=> response.json());
      }
    }

videoCenter.component.ts :(我订阅了getVideos（）方法）：



    import { Component, OnInit } from '@angular/core';
        import {Video} from '../video';
        import { VideoService } from '../video.service';
        @Component({
          selector: 'app-video-center',
          templateUrl: './video-center.component.html',
          styleUrls: ['./video-center.component.css'],
          providers:[VideoService]//,Http,HttpClientModule
        })
        export class VideoCenterComponent implements OnInit {
          myAllVideos:Array;//here I want to put my get Request Data
          constructor(private _videoService:VideoService) { }

          selectedVideo:Video;

          onSelectVideo (video:any){
            this.selectedVideo=video;
          }

          ngOnInit() {
            this._videoService.getVideos().subscribe(result => this.myAllVideos = result);
          }

        }

我跑的时候

node server.js

in VSCode terminal , then in POSTMAN app I can get all records by requesting GET in "localhost:3000/api/videos".But in my app, I am unable to load data which is running in 4200 port. When I click on button which loads video-center.component.ts , getVideos() is triggered in ngOnInit() but it throws this error: