The difference between isFinite() method and isFinite() function in JavaScript

July 8, 2020

JavaScript isFinite() Function

The isFinite() function determines whether a number is a finite, legal number. 

If  needed, the parameter is first converted to a number.

This function returns false if the value is +infinity, -infinity, or NaN (Not-a-Number), otherwise it returns true.



where testValue = The value to be tested for finiteness.


console.log(isFinite(1)) //true
console.log(isFinite(-1.99)) //true
console.log(isFinite(4-2)) //true
console.log(isFinite(0)) //true
console.log(isFinite("1")) //true
console.log(isFinite("string")) //false
console.log(isFinite("2020/5/5")) //false

JavaScript isFinite() Method

Checks whether a value is a finite number.

This method returns true if the value is of the type Number, and equates to a finite number. Otherwise it returns false.


Number.isFinite(1) //true
Number.isFinite(-1.1) //true
Number.isFinite(4-2) //true
Number.isFinite(0) //true
Number.isFinite('1') //false
Number.isFinite('String') //false
Number.isFinite('2020/5/5') //false
Number.isFinite(Infinity) //false
Number.isFinite(-Infinity) //false
Number.isFinite(0 / 0) //false

You must have noticed the difference.

If not, let me show here separately.

console.log(isFinite("1")) //true

Number.isFinite('1') //false

//in case you're thinking about quotes, they don't matter. You can use either one.

Almost everything is the same about the method and function, except one thing.

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

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


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