How to Validate Number String in JavaScript ?

Validating a number string in JavaScript involves ensuring that a given string represents a valid number. This typically includes checking for digits, optional signs (+/-), decimal points, and possibly exponent notation (e.g., "1.23e4"). We will use various methods to validate number strings in JavaScript like the isNaN Function, the Number() Function, and the isFinite Function.

Validating number string using the isNaN Function

In this approach for Validating number string the isNaN Function is used. The isNaN function returns true if the given value is NaN (Not-a-Number), and false otherwise. The function takes a string as input and returns true if it represents a valid number, as determined by the isNaN function. It returns false otherwise.

Example: Validate number string in JavaScript using the isNaN Function.

// Validate number string using isNaN function

function isValidNumberIsNaN(str) {
    return !isNaN(str);
}

console.log(isValidNumberIsNaN("123"));     
console.log(isValidNumberIsNaN("-1.23"));    
console.log(isValidNumberIsNaN("3.14e5"));   
console.log(isValidNumberIsNaN("abc"));    
console.log(isValidNumberIsNaN("123.45.67"));

true
true
true
false
false

Validating number string using the Number() Function

In this approach for Validating number string the Number() Function is used. The Number function converts the given value to a number. If the value cannot be converted to a valid number, it returns NaN. The r function first converts the input string to a number using the Number function. It then checks if the resulting value is NaN using the isNaN function, and returns false if it is NaN, indicating that the input string is not a valid number.

Example: Validate number string in JavaScript using the Number() Function.

// Validate number string using Number function

function isValidNumberNumber(str) {
    return !isNaN(Number(str));
}

console.log(isValidNumberNumber("123"));     
console.log(isValidNumberNumber("-1.23"));    
console.log(isValidNumberNumber("3.14e5"));    
console.log(isValidNumberNumber("abc"));     
console.log(isValidNumberNumber("123.45.67")); 

true
true
true
false
false

Validating number string using the isFinite Function

In this approach for Validating number string the isFinite Function is used. The isFinite function returns true if the given value is a finite number and false otherwise. The function takes a string as input and returns true if it represents a valid finite number, as determined by the isFinite function. It returns false otherwise

Example: Validate number string in JavaScript using the isFinite Function.

// Validate number string using isFinite function

function isValidNumberIsFinite(str) {
    return isFinite(str);
}


console.log(isValidNumberIsFinite("123"));      
console.log(isValidNumberIsFinite("-1.23"));    
console.log(isValidNumberIsFinite("3.14e5"));    
console.log(isValidNumberIsFinite("abc"));       
console.log(isValidNumberIsFinite("123.45.67")); 

true
true
true
false
false