Ember.js MutableArray firstObject 属性

Ember.js 是一个开源的JavaScript框架，用于开发基于Model-View-Controller（MVC）架构的大型客户端Web应用程序。Ember.js是最广泛使用的前端应用程序框架之一。它旨在加快开发速度并提高生产力。目前，许多网站都使用了Ember.js，包括Square，Discourse，Groupon，Linked In，Live Nation，Twitch和Chipotle。

firstObject 属性用于检索数组的第一个对象。

语法：

array.firstObject

返回值： 数组中的第一个对象。

要运行以下示例，您需要有一个ember项目。要创建一个项目，您需要首先安装ember-cli。在终端中编写以下代码：

npm install ember-cli

现在可以通过输入以下代码来创建项目：

ember new <project-name> --lang en

要启动服务器，请输入：

ember serve

示例1

输入以下代码以生成本示例的路线：

ember generate route richest-people

app/routes/richest-people.js

import Route from '@ember/routing/route'; 
import { sortBy } from '@ember/array'; 
  
export default class RichestPeopleRoute extends Route { 
    richestPeople = [ 
        { 'name': 'mukesh ambani', 'net-worth': 90.7 }, 
        { 'name': 'jeff Bezos', 'net-worth': 148.1 }, 
        { 'name': 'Warren Buffet', 'net-worth': 99.3 }, 
        { 'name': 'Bill gates', 'net-worth': 104.7 }, 
        { 'name': 'elon Musk', 'net-worth': 253.4 }, 
        { 'name': 'gautam adani and family',  
            'net-worth': 115.8 }, 
        { 'name': 'Larry Page', 'net-worth': 93.4 }, 
        { 'name': 'larryEllison', 'net-worth': 103.3 }, 
        { 'name': 'sergeyBrin', 'net-worth': 89.9 }, 
        { 'name': 'bernard Arnault and family',  
            'net-worth': 157.1 }, 
    ]; 
    firstPerson; 
    lastPerson; 
    idx = 5; 
    randomPerson; 
    num; 
    model() { 
        this.richestPeople =  
            this.richestPeople.sortBy('net-worth'); 
  
        this.randomPerson =  
            this.richestPeople[this.idx - 1]; 
        return this.richestPeople; 
    } 
    setupController(controller, model) { 
        this._super(controller, model); 
        controller.set('idx', this.idx); 
        controller.set('firstPerson',  
            this.richestPeople.firstObject); 
        controller.set('lastPerson',  
            this.richestPeople.lastObject); 
        controller.set('randomPerson',  
            this.randomPerson); 
        controller.set('richestPeople',  
            this.richestPeople); 
        controller.set('num',  
            this.richestPeople.length); 
    } 
}

app/controllers/richest-people.js

import Ember from 'ember'; 
  
export default Ember.Controller.extend({ 
    actions: { 
        setIdx(n) { 
            this.idx = parseInt(n); 
            this.set('randomPerson',  
                this.richestPeople[this.idx - 1]); 
        } 
    } 
})

app/template/richest-people.hbs

{{page-title "Richest People"}} 
  
<div> 
    <label>Enter Value (1-{{this.num}}):</label> 
    {{input value=this.idx}} 
</div> 
<div> 
    <input type="button" id="fetch" 
         value="Fetch" {{action 'setIdx' this.idx}}/> 
</div> 
<br> 
<div>First Person on the List: {{this.firstPerson.name}}  
      {{this.firstPerson.net-worth}} B 
</div> 
<br> 
<div>Last Person on the List: {{this.lastPerson.name}}  
      {{this.lastPerson.net-worth}} B 
</div> 
<br> 
<div>Random Person on the List: {{this.randomPerson.name}}  
      ${{this.randomPerson.net-worth}} B 
</div> 
  
{{outlet}}

输出： 访问 localhost:4200/richest-people 查看输出

Ember.js MutableArray firstObject 属性

示例2

在这个示例中，输入以下代码以生成路线：

ember generate route notepad

app/routes/notepad.js

import Route from '@ember/routing/route'; 
  
export default class NotepadRoute extends Route { 
    items = []; 
    empty = true; 
    item; 
    firstItem; 
    lastItem; 
    randomItem; 
    num; 
    model() { 
        this.firstItem = this.items.firstObject; 
        this.lastItem = this.items.lastObject; 
        this.num = this.items.length; 
        return this.items; 
    } 
    setupController(controller, model) { 
        this._super(controller, model); 
        controller.set('items', this.items); 
        controller.set('empty', this.empty); 
        controller.set('firstItem', this.firstItem); 
        controller.set('lastItem', this.lastItem); 
        controller.set('randomItem', this.randomItem); 
        controller.set('num', this.num); 
    } 
}

app/controllers/notepad.js

import Ember from 'ember'; 
import { pushObject } from '@ember/array'; 
  
export default Ember.Controller.extend({ 
    actions: { 
        addItem(item) { 
            this.items.pushObject(item); 
            this.set('empty', false); 
            this.set('firstItem', this.items.firstObject); 
            this.set('lastItem', this.items.lastObject); 
            this.set('num', this.items.length); 
            this.set('randomItem', this.items[ 
                Math.floor(Math.random() * this.num)]); 
        } 
    } 
})

app/template/notepad.hbs

{{page-title "Notepad"}} 
  
<h2>Notepad</h2> 
  
<div> 
    <label>Enter Item: </label> 
    {{input value=this.item}} 
</div> 
<div> 
    <input type="button" id="add-item" 
        value="Add Item" {{action 'addItem' this.item}}/> 
</div> 
<br/><br/> 
  
{{#if this.empty}} 
<div>The list is empty!</div> 
{{else}} 
<div> 
    <div>First Item: {{this.firstItem}}</div> 
    <div>Latest Item: {{this.lastItem}}</div> 
    <div>Random Item: {{this.randomItem}}</div> 
    <div>Number of Items: {{this.num}}</div> 
</div> 
{{/if}} 
  
<br/><br/> 
{{outlet}}