How Can I Check if a JavaScript String Represents a Valid Number?

Checking if a String Is a Valid Number

You can verify if a string contains a valid number in JavaScript using the following methods:

1. isNaN() Function

Use isNaN() to check if the variable is not a number, regardless of whether it's a string or a number:

const isNumeric = (str) => !isNaN(str);
console.log(isNumeric('123')); // true
console.log(isNumeric('abc')); // false

2. Numerical Conversion

Convert the string to a number using num:

const num = +str;
console.log(num); // 123 (if str is '123')
console.log(isNaN(num)); // false (if str is '123')

3. parseInt() Function

Extract a number from the beginning of the string using parseInt():

const num = parseInt(str, 10);
console.log(num); // 123 (if str is '123px')
console.log(isNaN(num)); // false (if str is '123px')

4. Notes on Specific Cases

• Empty strings are interpreted as 0 by num and isNaN(), but as NaN by parseInt().
• NaN and Infinity are considered numbers by isNaN().
• parseInt() treats decimals as integers, chopping off any fractional part.
• " num" converts strings with spaces or other non-numeric characters to 0. parseInt() treats such strings as NaN.

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