Javascript Angular4-如何检查Twitter媒体密钥是否存在或未定义

在…的基础上建造。。。我希望能够返回一个帐户的时间线的最后5条推文，以及他们可能附加的任何图像。我的问题是，在对Twitter的API进行搜索调用时，返回的一些tweet JSON根本不包含entities.media.media_url键。如果我将entities.media.media_url作为调用的一部分，并且tweet不包含任何附件，则会中断整个请求，并且根本不会呈现任何tweet。在呈现请求之前，是否可以检查tweet是否包含该信息？例如，在尝试解析这两条推文时：

tweet1（无图像）

tweet2（包含附加图像）

我有一个node.js后端处理搜索调用的大部分工作（以下）， 我的tweets.component.ts会抓取元素并将它们分配给前端要插值的变量

tweets.component.ts

import { Component, OnInit, Input } from '@angular/core';
import { NO_ERRORS_SCHEMA } from '@angular/core';
import { Ng4TwitterTimelineModule } from 'ng4-twitter-timeline/lib/index';
import { Ng4TwitterTimelineService } from 'ng4-twitter-timeline/lib/index';
import { Http, Headers } from '@angular/http';
import { NgModel, NgForm, FormsModule } from '@angular/forms';

@Component({
  selector: 'app-tweets',
  templateUrl: './tweets.component.html',
  styleUrls: ['./tweets.component.scss'],
})
export class TweetsComponent implements OnInit {

  searchquery = 'musechat';
  tweetsdata;
  screen_name;
  user;
  profile_img_url;
  user_id;

  asset_img_url;

  // icon = this.tweetsdata[0].user.entities.profile_image_url;
   constructor (private http: Http) {}

  ngOnInit() {
    this.makecall();
    this.searchcall();
  }

  makecall() {
    const headers = new Headers();

    headers.append('Content-Type', 'application/X-www-form-urlencoded');

    this.http.post('http://localhost:3000/authorize', {headers: headers}).subscribe((res) => {
      // console.log(res);
    });
  }

  searchcall() {
    const headers = new Headers();
    // const searchterm = 'query=' + this.searchquery;
    const searchterm = 'query=from%3Adailymuse%20%23' + this.searchquery;


    headers.append('Content-Type', 'application/X-www-form-urlencoded');

    this.http.post('http://localhost:3000/search', searchterm, {headers: headers}).subscribe((res) => {
      this.tweetsdata = [
        res.json().data.statuses[0],
        res.json().data.statuses[1],
        res.json().data.statuses[2],
        res.json().data.statuses[3],
        res.json().data.statuses[4],
        // res.json().data.statuses[5],
      ];

      console.log(this.tweetsdata);
      this.screen_name = this.tweetsdata[0].user.screen_name;
      this.user = this.tweetsdata[0].user.name;
      this.profile_img_url = this.tweetsdata[0].user.profile_image_url_https;
      this.user_id = this.tweetsdata[0].user.id_str;
    });
  }
 }
}

tweets.component.html

<div class="twitter-container">
    <div class="twitter-carousel">
        <div class="twitter-header">
            <a class="tw-header" href="http://twitter.com/intent/user?user_id={{user_id}}" target="_blank">
                <img class="twitter-icon" src={{profile_img_url}}>
                <span>{{user}}</span>
                <span class="twitter-screen">@{{screen_name}}</span>
            </a>
        </div>

        <hr>

        <div class="tweet-container">
            <div *ngFor="let item of tweetsdata" class="tweets-card">
                <div class="tweet-text">
                    <p class="tweet-date">{{item.created_at | slice:0:10}}</p>
                    <p>{{item.text}}</p>
                    <!-- <div *ngIf="item.entities.media[0].media_url" class="tweet-img"> -->
                    <!-- <img [src]=item.entities.media[0].media_url/> --> <!-- either of these break the code if there is a tweet that doesn't contain an attached image -->
                    <div>


                        <p>{{getImage()}}</p>

                    </div>

                    <div class="interact-tweet">
                        <a href="https://twitter.com/intent/tweet?in_reply_to={{item.id_str}}" target="_blank"><i class="fa fa-reply" aria-hidden="true"></i></a>
                        <a href="https://twitter.com/intent/retweet?tweet_id={{item.id_str}}" target="_blank"><i class="fa fa-retweet" aria-hidden="true"></i></a>
                        <a href="https://twitter.com/intent/like?tweet_id={{item.id_str}}" target="_blank"><i class="fa fa-heart" aria-hidden="true"></i></a>
                    </div>
                </div>
            </div>
        </div>

    </div>

</div>

{{item.created_at|slice:0:10}
{{item.text}

{{getImage（）}}

import { Component, OnInit, Input } from '@angular/core';
import { NO_ERRORS_SCHEMA } from '@angular/core';
import { Ng4TwitterTimelineModule } from 'ng4-twitter-timeline/lib/index';
import { Ng4TwitterTimelineService } from 'ng4-twitter-timeline/lib/index';
import { Http, Headers } from '@angular/http';
import { NgModel, NgForm, FormsModule } from '@angular/forms';

@Component({
  selector: 'app-tweets',
  templateUrl: './tweets.component.html',
  styleUrls: ['./tweets.component.scss'],
})
export class TweetsComponent implements OnInit {

  searchquery = 'musechat';
  tweetsdata;
  screen_name;
  user;
  profile_img_url;
  user_id;

  asset_img_url;

  // icon = this.tweetsdata[0].user.entities.profile_image_url;
   constructor (private http: Http) {}

  ngOnInit() {
    this.makecall();
    this.searchcall();
  }

  makecall() {
    const headers = new Headers();

    headers.append('Content-Type', 'application/X-www-form-urlencoded');

    this.http.post('http://localhost:3000/authorize', {headers: headers}).subscribe((res) => {
      // console.log(res);
    });
  }

  searchcall() {
    const headers = new Headers();
    // const searchterm = 'query=' + this.searchquery;
    const searchterm = 'query=from%3Adailymuse%20%23' + this.searchquery;


    headers.append('Content-Type', 'application/X-www-form-urlencoded');

    this.http.post('http://localhost:3000/search', searchterm, {headers: headers}).subscribe((res) => {
      this.tweetsdata = [
        res.json().data.statuses[0],
        res.json().data.statuses[1],
        res.json().data.statuses[2],
        res.json().data.statuses[3],
        res.json().data.statuses[4],
        // res.json().data.statuses[5],
      ];

      console.log(this.tweetsdata);
      this.screen_name = this.tweetsdata[0].user.screen_name;
      this.user = this.tweetsdata[0].user.name;
      this.profile_img_url = this.tweetsdata[0].user.profile_image_url_https;
      this.user_id = this.tweetsdata[0].user.id_str;
    });
  }
 }
}

<div class="twitter-container">
    <div class="twitter-carousel">
        <div class="twitter-header">
            <a class="tw-header" href="http://twitter.com/intent/user?user_id={{user_id}}" target="_blank">
                <img class="twitter-icon" src={{profile_img_url}}>
                <span>{{user}}</span>
                <span class="twitter-screen">@{{screen_name}}</span>
            </a>
        </div>

        <hr>

        <div class="tweet-container">
            <div *ngFor="let item of tweetsdata" class="tweets-card">
                <div class="tweet-text">
                    <p class="tweet-date">{{item.created_at | slice:0:10}}</p>
                    <p>{{item.text}}</p>
                    <!-- <div *ngIf="item.entities.media[0].media_url" class="tweet-img"> -->
                    <!-- <img [src]=item.entities.media[0].media_url/> --> <!-- either of these break the code if there is a tweet that doesn't contain an attached image -->
                    <div>


                        <p>{{getImage()}}</p>

                    </div>

                    <div class="interact-tweet">
                        <a href="https://twitter.com/intent/tweet?in_reply_to={{item.id_str}}" target="_blank"><i class="fa fa-reply" aria-hidden="true"></i></a>
                        <a href="https://twitter.com/intent/retweet?tweet_id={{item.id_str}}" target="_blank"><i class="fa fa-retweet" aria-hidden="true"></i></a>
                        <a href="https://twitter.com/intent/like?tweet_id={{item.id_str}}" target="_blank"><i class="fa fa-heart" aria-hidden="true"></i></a>
                    </div>
                </div>
            </div>
        </div>

    </div>

</div>

if (entities.media) // Code if it exists here
else // Code if it doesn't here