Number Validation in JavaScript (original) (raw)

Last Updated : 03 Jan, 2025

Here are the various methods to validate numbers in JavaScript

1. Check if a Value is a Number

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

JavaScript `

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.

2. Check if a String is Numeric

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

JavaScript `

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.

3. Validate Integer

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

JavaScript `

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.

4. Validate Floating-Point Numbers

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

JavaScript `

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.

5. Range Validation

Ensure a number falls within a specific range.

JavaScript `

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.

6. Regex for Strict Validation

Use regular expressions for specific number formats.

JavaScript `

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.

7. Validate Positive Numbers

Check if a number is positive.

JavaScript `

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.

8. Validate Negative Numbers

Check if a number is negative.

JavaScript `

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.

9. Validate Even Numbers

Determine if a number is even.

JavaScript `

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.

10. Validate Odd Numbers

Check if a number is odd.

JavaScript `

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.