isNaN、Number.isNaN、isFinite、Number.isFinite

isNaN和Number.isNaN

Both of these are used to determine whether the parameter is of type NaN.

The implementation principle of isNaN is: through the Number() method, try to convert the parameter into a Number type . If it succeeds, it returns false, and if it fails, it returns true.

isNaN just judges whether the incoming parameter can be converted into a number, not strictly judges whether the parameter is equal to NaN .

And Number.isNaN() will judge whether the incoming parameter is a number type (NaN is also a special number type) and whether it is strictly equal to NaN (===).

console.log(isNaN('123')) //fasle，字符串类型的123能转成数字，所以返回false
console.log(Number.isNaN('123')) //false，字符串类型的123不是NaN，所以返回false
console.log(Number.isNaN(123) // false
console.log(isNaN('NaN')) // true
console.log(isNaN('nAn')) // true
console.log(isNaN('测试')) //true  因为Number(字符串)会返回NaN
console.log(Number.isNaN('测试')) //false，字符串不是NaN，所以返回false
console.log(Number.isNaN(NaN)) //true

isFinite、Number.isFinite

Both methods are used to determine whether the parameter is finite or not.

When the parameter is positive infinity ( Number.POSITIVE_INFINITY and Infinity ), negative infinity ( Number.POSITIVE_INFINITY and -Infinity ), NaN. return false

The difference between isFinite and Number.isFinite is the same as above, and the default parameter of Number.isFinite is a number type. And IsFinite will convert the parameter to a numeric type before judging.

For the Number.isFinite() method. The following two points must be met to return true.

• The parameter is numeric,

• Argument is not infinite/small or NaN

console.log(Number.isFinite('123'))// false
console.log(Number.isFinite('abc')) //fasle
console.log(Number.isFinite(NaN)) // false
console.log(Number.isFinite(1)) // true

 console.log(isFinite('123')) //true
 console.log(isFinite('abc')) // fasle 因为Number('abc')是NaN
console.log(isFinite(NaN)) // false 同上
console.log(isFinite(-Infinity )) // false 因为Number(-Infinity)为-Infinity

Notice

Number(null) // 0
Number('') // 0
console.log(isFinite(null ))  //true