1 + undefined的结果是什么 [英] what's the result of 1 + undefined

问题描述

1 + undefined = ?  

1. 首先，String(未定义)获取字符串"undefined"
2. 秒，1 +"undefined" ="1undefined"

怎么了?

我在chrome控制台中运行它，它返回 NaN .

I run it in chrome console ,it return NaN.

您能解释一下结果吗?

我认为它应该是"1undefined".tks

I think it should be "1undefined". tks

推荐答案

NaN 是失败的 Number 操作的结果.

NaN is the result of a failed Number operation.

1 + undefined           // NaN
"1" + undefined         // "1undefined"
1 + "" + undefined      // "1undefined"
1 + ("" + undefined)    // "1undefined"
typeof NaN              // "number"
typeof undefined        // "undefined"
NaN === NaN             // false (it's not reflexive!)
undefined === undefined // true (it's reflexive)
NaN.toString()          // "NaN"

NaN 表示非数字，该数字应为预期的数字.使用 NaN 的任何Number运算也将导致 NaN .

NaN means Not a Number where a number was expected. Any Number operation with NaN will result in NaN as well.

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