Angular项目中带或不带export关键字的类和接口

Question

我正在学习角度，选择了一个视频课程和一本pdf书，现在我对“出口”关键字的使用感到困惑...

两门课的一个例子来展示我的困惑...我只需要朝正确的方向快速踢一脚，就能克服这个小障碍。

Visual Studio 2017

示例项目使我在clientapp/app文件夹中创建了一个接口文件夹，并在其中放置了一个接口“answer.ts”。这是没有关键字“导出”。

interface IAnswer {
    Id: number;
    QuestionId: number;
    Text: string;
    Value: number;
}

import { Component, Inject, Input, OnChanges, SimpleChanges } from "@angular/core";
import { Router } from "@angular/router";
import { HttpClient } from "@angular/common/http";

@Component({
    selector: "answer-list",
    templateUrl: "./answer-list.component.html",
    styleUrls: ["./answer-list.component.css"]
})

export class AnswerListComponent implements OnChanges {
    @Input() question: IQuestion;
    answers: IAnswer[];
    title: string;

    constructor(private http: HttpClient,
        @Inject("BASE_URL") private baseUrl: string,
        private router: Router) {

        this.answers = [];
    }

    ngOnChanges(changes: SimpleChanges) {
        if (typeof changes['question'] !== "undefined") {
            //alert(1);
            // retrieve the question variable change info
            var change = changes['question'];

            // only perform the task if the value has been changed
            if (!change.isFirstChange()) {
                // execute the Http request and retrieve the result
                this.loadData();
            }
        }
    }

    loadData() {
        var url = this.baseUrl + "api/answer/All/" + this.question.Id;
        this.http.get<IAnswer[]>(url).subscribe(res => {
            this.answers = res;
        }, error => console.error(error));
    }
}

export class Recipe {
    constructor(public name: string, public description: string, public imagePath: string){
    }
}

import { Recipe } from "../../recipes/recipe.model";

@Injectable()
export class DataStorageService {
    getRecipes(){
        //get a authentication token
        const token = this.authService.getToken();
        const tokenQuery = '?auth=' + token

        this.http.get(this.recipesNode + tokenQuery)
        .pipe(
            map(
                (response: Response) => {
                    //we saved array of recipes 
                    const recipes: Recipe[] = response.json();
                    return recipes;
                }
            )
        )
        .subscribe(
            (recipes: Recipe[]) => {
                this.recipeService.setRecipes(recipes);
            }
        );
    }
}

Answer 1

它取决于项目中的compileroptions集。您可以强制系统期待或不期待export。通常，这个决定是根据以下问题做出的：是使用WebPack、Browserify还是其他模块化加载器，还是只想将给定的*.ts-文件转换为*.js-文件。请看一下这个帖子：

未定义TypeScript导出