Angular 2的块作用域变量问题

我目前正在使用TypeScript运行Angular 2的演示。这里有两个文件:作为模板导入的index.html文件和TypeScript文件。TypeScript文件编译成一个pomodoro-timer.js，对于这个演示，所有的类都包含在一个文件中:

pomodoro-timer.ts

import {
    Component,
    Input,
    Pipe,
    PipeTransform,
    Directive,
    OnInit,
    HostListener
} from '@angular/core';
import { bootstrap } from '@angular/platform-browser-dynamic';
/// Model interface 
interface Task {
    name: string;
    deadline: Date;
    queued: boolean;
    pomodorosRequired: number;
}
/// Local Data Service
class TaskService {
    public taskStore: Array<Task> = [];
constructor() {
    const tasks = [
        {
            name: "Code an HTML Table",
            deadline: "Jun 23 2015",
            pomodorosRequired: 1
        },
        {
           name: "Sketch a wireframe for the new homepage",
           deadline: "Jun 24 2016",
           pomodorosRequired: 2
        },
        {
            name: "Style table with Bootstrap styles",
            deadline: "Jun 25 2016",
            pomodorosRequired: 1
        },
        {
            name: "Reinforce SEO with custom sitemap.xml",
            deadline: "Jun 26 2016",
            pomodorosRequired: 3
        }
    ];
    this.taskStore = tasks.map(task => {
        return {
            name: task.name,
            deadline: new Date(task.deadline),
            queued: false,
            pomodorosRequired: task.pomodorosRequired
        };
    });
}
/// Component classes 
/// - Main Parent Component
@Component({
    selector: 'pomodoro-tasks',
    styleUrls: ['pomodoro-tasks.css'],
    templateUrl: 'pomodoro-tasks.html'
})
class TasksComponent {
    today: Date;
    tasks: Task[];
    constructor() {
        const TasksService: TasksService = new TasksService();
        this.tasks = taskService.taskStore;
        this.today = new Date();
    }
};
bootstrap(TasksComponent);

index . html

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>Hello Angular 2!</title>
        <!-- required stylesheets -->
        <link rel="stylesheet" href="node_modules/bootstrap/dist/css/bootstrap.min.css" />
        <!-- required javascripts -->
        <script src="node_modules/es6-shim/es6-shim.min.js"></script>
        <script src="node_modules/zone.js/dist/zone.js"></script>
        <script src="node_modules/reflect-metadata/Reflect.js"></script>
        <script src="node_modules/systemjs/dist/system.js"></script>
        <script src="node_modules/rxjs/bundles/Rx.js"></script>
        <script src="systemjs.config.js"></script>
        <script>
            // importation of component module
            // with no file extension
            System.import('built/pomodoro-tasks').then(null, console.error.bind(console));
        </script>
    </head>
    <body>
        <nav class="navbar navbar-default navbar-static-top">
            <div class="container">
                <div class="navbar-header">
                    <strong class="navbar-brand">My Pomodoro Tasks</strong>
                </div>
            </div>
        </nav>
        <pomodoro-tasks></pomodoro-tasks>
    </body>
</html>

一切似乎都很好，然而，的这一部分的pomodoro定时器。ts文件似乎抛出了一个错误:

class TasksComponent {
    today: Date;
    tasks: Task[];
    constructor() {
        // (Cannot find name 'TasksService'.at line 91 col 29, BELOW)
        // (Block-scoped variable 'TasksService' used before its declaration.at line 91 col 48, BELOW)
        const TasksService: TasksService = new TasksService();
        // (Cannot find name 'taskService'.at line 92 col 22, BELOW)
        this.tasks = taskService.taskStore;
        this.today = new Date();
    }
};
bootstrap(TasksComponent);

熟悉TypeScript的人知道为什么我会得到这些错误吗?我正在使用Atom IDE与TypeScript插件。

如果像这样初始化对象

const TasksService: TasksService = new TasksService();

您将收到以下错误，

Blocked-scoped variable 'TasksService' used before its declaration.

要解决此问题，请将变量名更改为其他内容，如

const TaskServ: TasksService = new TasksService();

注意:这个错误通常发生在你声明一个与类(Object)同名的变量时。

1)首先你有一个错误taskService而不是tasksService

2)你不应该像你在这里所做的那样实例化TasksService。

constructor() {
  const TasksService: TasksService = new TasksService();
  this.tasks = taskService.taskStore;
  this.today = new Date();
}

你应该把代码改成

constructor(private taskService:TasksService) {
  this.tasks = this.taskService.taskStore;
  this.today = new Date();
}

要了解更多有关依赖注入和最佳实践的信息，请查看此链接https://angular.io/docs/ts/latest/guide/dependency-injection.html

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