javascript - isNaN 如何验证此代码中 Prompt 仅返回字符串的值？

Question

据我所知，Prompt 只返回 String 类型的值。那么，下面的代码如何正常工作呢？

var a = prompt('Number or String? Verify now!');

if(!isNaN(a)){
  alert('This is number.');
}
else alert('This is string.')

Answer 1

来自https://www.w3schools.com/jsref/jsref_isNaN.asp , 全局 isNaN() 函数，将测试值转换为数字，然后进行测试。

The isNaN() function determines whether a value is an illegal number (Not-a-Number).

This function returns true if the value equates to NaN. Otherwise it returns false.

This function is different from the Number specific Number.isNaN() method.

The global isNaN() function, converts the tested value to a Number, then tests it.

Number.isNaN() does not convert the values to a Number, and will not return true for any value that is not of the type Number.