>[warning] typeof运算符 --- JS是弱类型语言, 在运行时会判断类型, 利用typeof可以打印出对应的类型, 使用方式 * typeof(表达式) * typeof 变量 结果如下 | 示例 | 结果 | 运行时类型 | | --- | --- | --- | | "ok" | string | String | | 3 | number | Number | | true | boolean | Boolean | | undefined | undefined | undefined | | null | object | Null | | {} | object | Object | | [] | object | Array | | Symbol() | symbol | Symbol | | NaN | number | NaN | | (function(){}) | function | Object | 需要特殊记忆, null -> object, 引用都是object, NaN -> number