打字稿-变量声明 [英] Typescript - variables declaration

问题描述

我不确定这是否是解决此问题的地方，但有人告诉我代码审查不是解决问题的地方.

I'm not sure if this is the place for this question, but I've been told code review is not the place for it.

我只是在学习Angular 2和Typescript，所以正在研究以下教程:

I'm just learning Angular 2 and Typescript, so am working through this following tutorial:

https://angular.io/docs/ts/latest/tutorial/toh-pt4.html

在第三部分和第四部分之间，app.component.ts中的heroes变量的声明从以下内容更改:

Between part three and four, the declaration of the heroes variable in the app.component.ts changes from:

export class AppComponent {
    heroes = HEROES;
}

收件人:

export class AppComponent {
    heroes: Hero[];
}

我了解第一个将其设置为常量的heroes数组，但是为什么第二个使用冒号而不是仅将其设置为空数组?

I understand the first one sets it to a constant of heroes array but why does the second one use a colon and not just set it to an empty array?

将第二个更改为=实际上会引发表达式期望错误，因此基本上我只是想了解两者之间的差异.

Changing the second one to an = actually throws an expression expected error so basically I'm just trying to understand the differences between the two.

推荐答案

heroes: Hero[];

未将其设置为值. 它只是用

doesn't set it to a value. It just defines a property with

• 名称= heroes
• type = Hero[]表示Hero
的数组
• 不分配值将其保留为默认值null.

• name = heroes
• type = Hero[] which means array of Hero
• without assigning a value which keeps it at default value null.

通过初始化，它看起来像

With initialization it would look like

heroes: Hero[] = [new Hero('Spidey'), new Hero('Batman')];

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