(JS) isnan() method determines the reason why undefined is true

Use isNaN() Judgment is not NaN when , This method is used Number() Method to make a conversion , Any non number is cast ,undefined Converted to NaN, So show true

console.log(isNaN(undefined)) //true

isNaN() Conversion except null And array types are converted to numbers 0 outside , Other non numeric types will be converted to NaN
character string

console.log(isNaN("qigeyu")) //true

object

console.log(isNaN({
    })) //true