typescript关于void的问题

Question

翻阅了一下ts的教程是说void声明一个变量的时候只有两个值：undefined、null，
无论是英文教程还是中文教程都是这么写的，但是当我写一个最基本的例子时，编译却保错，代码如下：

let unusable: void=null;  // Type 'null' is not assignable to type 'void'.

值为undefined时就没问题

let unusable: void=undefined;

这是为什么？

Answer 1

void

However, when using the --strictNullChecks flag, null and undefined are only assignable to any and their respective types (the one exception being that undefined is also assignable to void).

是不是开了这个 ....

Answer 2

首先我这里let unusable: void=null;是不报错的，有图为证，不知道你用的是那个版本

By default null and undefined are subtypes of all other types.
That means you can assign null and >undefined to something like number.