> For the complete documentation index, see [llms.txt](https://xiaohesong.gitbook.io/today-i-learn/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://xiaohesong.gitbook.io/today-i-learn/front-end/basic.md).

# basic

* `NaN`

  这个得字面意思就是"Not a Number"。但是这个描述的并不是很好。把它描述成"无效的数字"反而会好点。 参考[这里](https://github.com/xiaohesong/TIL/blob/master/front-end/javascript/you-dont-known-js/types%26grammer/Chapter2-Values.md#special-numbers)
* `==` vs `===`

  大多数书籍中对于这两者的描述通常是：`==`是判断值是否相等，`===`是判断值和类型是否都相等。 这个说法是 **错误** 的。 更准确的说：“`==`允许在比较中强制，`===`不允许强制。” 参考[这里](https://github.com/xiaohesong/TIL/blob/master/front-end/javascript/you-dont-known-js/types%26grammer/Chapter4-coercion.md#loose-equals-vs-strict-equals)

## 原始类型和引用类型的区别

* 可变性
  * 原始类型不可变
  * 引用类型可变
* 存储位置
  * 原始存储在栈中, 存储的变量直接访问的位置。
  * 引用类型存储在堆中， 存储的是变量的位置，他指向引用对象在内存中的位置。
* 比较
  * 原始类型直接对值进行比较
  * 引用类型在某些情况下会进行类型转换成初始类型(==, >, <, ...)


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