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Number Validation in JavaScript - GeeksforGeeks

Last Updated : 15 Jul, 2025

Here are the various methods to validate numbers in JavaScript

Use typeof and isNaN() to determine if a value is a valid number.

const isNum = n =>
	typeof n === 'number' && !isNaN(n);

console.log(isNum(42)); 
console.log(isNum('42'));
console.log(isNum(NaN));

In this example

• typeof n === 'number' checks if the type of n is a number.
• !isNaN(n) ensures the value is not NaN (Not a Number).
• It ensures both type and value validity.

Use regular expressions or isFinite() to validate numeric strings.

const isNumStr = s => 
	!isNaN(s) && isFinite(s);

console.log(isNumStr('123'));
console.log(isNumStr('123abc')); 
console.log(isNumStr('1.23')); 

In this example

• !isNaN(s) ensures the string can be parsed as a number.
• isFinite(s) ensures the value is not infinite.
• This works for integers and decimals.

Check if a number is an integer using Number.isInteger().

const isInt = n => Number.isInteger(n);

console.log(isInt(42)); 
console.log(isInt(3.14));
console.log(isInt('42'));

In this example

• Number.isInteger(n) directly validates if n is an integer.
• It doesn't convert strings or other types to numbers.
• The function is simple and precise.

Use a combination of checks to ensure a number is a float.

const isFloat = n =>
	typeof n === 'number' && !Number.isInteger(n);

console.log(isFloat(3.14));
console.log(isFloat(42));
console.log(isFloat('3.14'));

In this example

• typeof n === 'number' ensures the value is a number.
• !Number.isInteger(n) confirms it's not an integer.
• This validates numbers with decimal points.

Ensure a number falls within a specific range.

const inRange = (n, min, max) =>
	n >= min && n <= max;

console.log(inRange(10, 5, 15));
console.log(inRange(20, 5, 15));
console.log(inRange(5, 5, 15));

In this example

• The function checks if n is greater than or equal to min and less than or equal to max.
• It’s a quick way to validate ranges.

Use regular expressions for specific number formats.

const isStrict = s => /^-?\d+(\.\d+)?$/.test(s);

console.log(isStrict('123'));
console.log(isStrict('-123.45'));
console.log(isStrict('abc123')); 

In this example

• The regex ^-?\d+(\.\d+)?$ checks for optional negative signs, digits, and decimals.
• This ensures strict numeric validation for strings.

Check if a number is positive.

const isPos = n => 
    typeof n === 'number' && n > 0;

console.log(isPos(42));
console.log(isPos(-42));
console.log(isPos(0));

In this example

• typeof n === 'number' ensures the input is a number.
• n > 0 validates that the number is positive.
• It excludes zero and negative numbers.

Check if a number is negative.

const isNeg = n => 
    typeof n === 'number' && n < 0;

console.log(isNeg(-42));
console.log(isNeg(42));
console.log(isNeg(0));

In this example

• typeof n === 'number' ensures the input is a number.
• n < 0 checks if the number is negative.
• It excludes zero and positive numbers.

Determine if a number is even.

const isEven = n => 
    typeof n === 'number' && n % 2 === 0;

console.log(isEven(4));
console.log(isEven(7));
console.log(isEven(-2));

In this example

• typeof n === 'number' ensures the input is a number.
• n % 2 === 0 checks if the remainder is zero when divided by 2.
• It works for both positive and negative numbers.

Check if a number is odd.

const isOdd = n => 
    typeof n === 'number' && n % 2 !== 0;

console.log(isOdd(7));
console.log(isOdd(4));
console.log(isOdd(-3));

In this example

• typeof n === 'number' ensures the input is a number.
• n % 2 !== 0 checks if the remainder is not zero when divided by 2.
• It works for both positive and negative numbers.

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